The Great Thrust Vector Debate


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1911Tuner
August 18, 2004, 09:11 AM
Okay...here it is. I ask that everyone hold their comments until Mr. Keenan
has made his counterpoint. This one promises to be interesting, as it has in the past. I fully expect it to be resolved with an agreement to disagree.
We'll leave it to the readers as to which theory to accept.

Any attempt to hijack the thread or take it off-topic will be deleted in good humor and fellowship. This is a debate of theories only. If anyone has a topic-related point of interest that may cause either one of us to change our outlook, it's more than welcome as long as it's kept factual and civil.

Enjoy!
___________________________________

A few years back, I read an article by Jerry Kuhnhausen on how the 1911 pistol really works. It was a good article, with excellent illustrations...but
when I got to the "Balanced Thrust Vector" part, I couldn't believe that a man as knowledgeable as Kuhnhausen could write that. However...The more I study on it, the more I think that he might have nailed it, and an
incredible experiment that was done by our own Jim Keenan was what
got me really thinking about it on a deeper level.

The gun is recoil operated. No question about it...but what initiates the recoil sequence? The bullet passing through the barrel...or the expansion of the gasses?

The expanding gasses generate the thrust needed for bullet movement.
Moreover, that thrust operates in all directions...not just forward. It pushes
the bullet and the slide equally...and it also generates equal thrust up, down, sideways, and diagonally. All directions.

The accepted theory is that the slide won't move unless the bullet moves, and that's absolutely true...but the question is why the slide will only move with bullet movement. Is the bullet really generating the recoil impulse...
or is the bullet merely a launching pad for the gasses...just like the
breechface of the slide? Two solid objects with an equally applied
force between them creates Kuhnhausen's Balanced (equal) Thrust vector.

Jim's experiment entailed threading the muzzle of the barrel and using a steel rod to keep the bullet static with a set screw in the muzzle. When the
round was fired, the bullet couldn't move at all, and neither did the slide.
Okay...No bullet movement means no slide movement.

Looking at it a little closer makes me understand that with the rod against the bullet and a set screw preventing the rod and bullet from moving, it prevented slide movement because the thrust generated by the gasses was transferred directly to the barrel, forcing it forward.

The barrel is mechanically locked to the slide via the locking lugs, and the slide can't move under those conditions...not because the bullet couldn't move, but because it was locked to the slide under extreme pressure. It's rather like locking your fingers in front of your chest and pulling equally in opposite directions. An isometric lock that won't allow movement UNTIL
the force becomes UNEQUAL.

So...The equal thrust is pushing rearward on the slide through the cartridge case at the same time that it's pushing on the bullet that is static in the barrel because of the rod and screw...and you have an isometric lock
that would be the same as welding the muzzle to a heavy steel block and pulling rearward on the frame of the gun while trying to manually operate the slide.

Keeping in mind that the bullet is a tight fit in the barrel when the gun is fired normally. The bullet is forced through the barrel under pressure,
and the barrel is forced forward under this pressure, maintaining the mechanical lockup to the slide...and nothing CAN move UNTIL something
happens to break the bullet's grip on the barrel.

When the bullet is pushed out of the case and down the bore, there is no isometric lock between barrel and slide. The thrust pushes backward on the slide at the same time that the bullet is moving, and imparts momentum to the slide which causes the slide and barrel to move rearward together in the same direction, rather than trying to pull them apart.

The bullet exits the barrel, and breaks the friction between it and the bore,
which frees up the barrel from its forward thrust. The momentum that was imparted to the slide takes over and completes the recoil cycle by pulling the now-free barrel along with the slide.

Mr. Keenan? Your counterpoints?

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1911Tuner
August 18, 2004, 10:58 AM
Btt with a link to view Kuhnhausen's article. It'll take the illustrations a few minutes to download, so be patient, fer cryin' out loud!:D

http://www.m1911.org/locking.htm

Grump
August 18, 2004, 11:15 AM
Simple. Pressure is irrelevant. Movement of mass is. Bullet moves forward, contributes to recoil. Gases move forward, contribute a bit more to recoil.

*THAT'S* why my 125-gr reloads with a 20.5 gr load of WW296 going 1350+ fps kick just as hard as 140-gr loads using 10 gr of (Yikes-what powder was it???) something else going about the same speed.

The internal ballistics term is "recoil ejecta." It's just physics. There's a tiny bit of gas-thrust recoil after the bullet leaves, but that is also a function of the gas mass and the gas velocity.
o...The equal thrust is pushing rearward on the slide through the cartridge case at the same time that it's pushing on the bullet that is static in the barrel because of the rod and screw...and you have an isometric lock
Well, you can get the same lockup that's never unlocked by taking a slide assembly, suspending it on strings, then snapping some means to get the firing pin up to ignition speed. Pressure stays the same and all that, the bullet will go forward, but allowing both the barrel and the slide to recoil together without any resistance to the barrel (the link connected to the frame), the thing stays locked tight. Gas pressure is irrelvant. The only "forward" thrust on the barrel is bullet friction in the bore, and any measurement of that force from slugging barrels will undoubtedly prove far less than 18,000+ psi times 1/2 times .45 times 3.14146....

Darkside
August 18, 2004, 12:20 PM
Question.....Since the bullet wasn't allowed to move, the gasses of the combustable solid powder couldn't expand and burn properly. Could the powder have just set there and smoldered until compleatly burned up? The powder wouldn't have reached anything near full preasure if this happened.

I have wondered about this????

Darkside

Grump
August 18, 2004, 01:18 PM
Darkside, it's actually quite the opposite. Nitrocellulose/nitroglycerine in a burning situation burns faster under higher pressure. Even in the roomy .45 ACP case, I would have expected such a closed-breech experiment *with a normal powder charge* to blow the chamber steel, or at least the casehead.

1911Tuner
August 18, 2004, 01:40 PM
Grump said:

Pressure stays the same and all that, the bullet will go forward, but allowing both the barrel and the slide to recoil together without any resistance to the barrel (the link connected to the frame),
__________________

Flawed theory. The thrust works equally in all directions. If the bullet and slide/barrel assembly were of equal mass, they would be propelled at the same rate of acceleration in opposite directions. The barrel is forced to unlock from the slide by the link after the barrel has traveled rearward for the distance required to get the slidestop pin out from under the lug. Until that happens, the link can pull until it snaps, and it won't unlock the barrel. The slide and barrel suspended on a string would remain locked on ignition because of the equal thrust in both directions. There is no link attached to the frame to force the barrel to change its rearward direction to a downward direction.

Suspend a firecracker in the geographic center between two tin cans.
When it explodes, both cans will be propelled equally in opposite directions, assuming instantaneous ingition of the firecracker rather than a progressive burn from one end to the other.

So...Does the barrel recoil and push on the slide...or does the slide recoil and pull on the barrel? Chicken or egg...Chicken or egg...

pauli
August 18, 2004, 01:43 PM
for every action, there is an equal and opposite reaction.

for every pressure propelled bullet, there is a pressure propelled casing (and, in this case, a breechface and all the rest).

of course, there are still expanding gasses exerting pressure on the casing after the bullet leaves the barrel... albeit briefly.

an interesting experiment would be to yank the bullet from the chambered round in a manner duplicating the velocity pattern of a real fired round.

1911Tuner
August 18, 2004, 01:50 PM
pauli! Yes!

A theoretical experiment for everybody to consider :

IF...you could attach a cable to the bullet and yank it through the bore at
the same rate of acceleration as it would have when it's PUSHED through the bore by the expanding gasses WITHOUT the benefit of those gasses
exerting thrust in both directions...would the slide and barrel move backward? I don't think so. I believe that the barrel would be pulled
forward until the bullet exited, and that the slide wouldn't move.

Tamara
August 18, 2004, 02:04 PM
So...Does the barrel recoil and push on the slide...or does the slide recoil and pull on the barrel?

B.

That's why they call it "boltface (or breechface) thrust." :)

(Even guns with fixed barrels get that slide moving rearward just fine, like the NGC(?) gas-delayed conversions of the 1911 that have the bbl fixed in place. :cool: )

Ktulu
August 18, 2004, 02:13 PM
IF...you could attach a cable to the bullet and yank it through the bore...would the slide and barrel move backward? I don't think so.

Right on!

EDITED TO ADD: Great thread!

1911Tuner
August 18, 2004, 02:13 PM
Tamara! YEEESSS!!!!! Exactimundo! There is a thrust vector
that imposes both against the base of the bullet and on the breechface
through the case head.

Where's Keenan at? :scrutiny:

JAREDSHS
August 18, 2004, 04:21 PM
way too much spare time on our hands here!!!lol

Grump
August 18, 2004, 04:51 PM
Hold it!!! Pressure = Thrust???

Don't think so. Rocket engines got pressure out the wazoo, in all directions, inside. But the thrust is only in the direction opposite the outgoing gas jet. As the bullet accelerates down the bore, thrust is generated in only one direction, although pressure is directed everywhere. The only forward thrust on the barrel is what the bullet imparts from friction drag...and that must be far less than the recoil impulse going in the opposite direction. Recoil impulse before unlocking is transferred from the slide to the barrel through the lockin surfaces.

So, my bottom line is that I see no NET forward thrust on the barrel because the recoil impulse caused by powder plus bullet accelerating far exceed the forward friction drag. That gas pressure going forward only "pushes" the barrel to the extent and limit of the drag.

Consider this experiment--hang a barrel with chambered round by strings. Heat the primer until it lights. See what happens. If the case can resist blowing out or rupturing long enough to get the bullet very far down-bore (maybe 3/4 an inch?), then you will have rearward recoil. If the case blows and the bullet stays put, the accelerating case and gases will give "forward" recoil.

1911Tuner
August 18, 2004, 05:18 PM
Uh...Grump. I ain't a rocket scientist, so i can't explain jet propulsion to any degree of accuracy. The "thrust" that I speak of is against
the bolt face and the base of the bullet equally...as well as up, down, sideways, etc. The pressure of the expanding gasses creates that thrust
between the two solid objects..The vector. Each one is the launching pad
for the other, and each one resists movement as a function of its own
different mass....thus the difference in acceleration from a standstill.

An experiment that can be don to illustrate the theory.

Find a short length of PVC pipe and a rubber ball that will fit the ID
fairly snugly. Punch a hole in the ball and attach a 100-foot cord.
Tie the cord to the bumber of a car and have a friend accelerate the car
until the slack comes out of the cord and pulls the ball out of the pipe.

Will the pipe "kick" while the ball is still inside it? No. You'll have to hang on tight to keep the pipe from being yanked out of your hands. You'll
move rearward only after the ball has exited, and only because of your resistance to the forward movement of the pipe. Rather like playing tug of war with somebody who suddenly lets go of the rope.

Jim Watson
August 18, 2004, 06:59 PM
Ever seen a Schwartzlose blow-forward pistol?

The breechface is a solid part of the receiver, the barrel is free to move forward against a spring. Fire the shot, the bullet goes forward, dragging the barrel forward with it by friction. The bullet departs the muzzle and the recoil spring drives the barrel backwards, scooping a fresh round out of the magazine. Recoil is said to be very heavy, as .32s go.

Carbine Williams designed a rifle with forward moving barrel. It, too, was said to be a hard kicker because you were moving both barrel and bullet forward at the shot, so the receiver and butt had to move backward all the harder. I 'spect it did a good deal of jumping around as the barrel returned.

Newton's Law sez that momentum must be conserved, with equal and opposite reactions. He doesn't say how.

Put a rod down the barrel of a 1911. Push against the breechface. The barrel and slide move rearward to unlock and separate from the force just like in firing where the force on the casehead (force = pressure x area) drives the slide back and the bullet forward. Opposing forces to the handle of the rod and the butt of the gun balance out. Momentum transfer is miniscule because you are not pushing that rod very fast.

In firing, pressure drives the bullet forward so the same pressure pushes the slide rearward to balance the momentum. Cause and effect. Can't separate them.

RJ357
August 18, 2004, 07:24 PM
When the bullet is immobilized in the barrel, the forward and rearward forces are equal and opposite and cancel. There is no net force in either direction. In that case, the high pressure gas exerts a force on the breechface and through the slide, the barrel. The gas also exerts an equal force against the bullet base, and against the barrel which it is locked to. Nothing moves. A similar situation exists in a cylinder of high pressure gas. The cylinder doesn't move either.

While it is true that the bullet needs to move forward in order for recoil to exist, that is not the direct cause of the recoil. Back to the cylinder of high pressure gas, it just sits there, as the pressure is equal in all directions. Now we take a hammer and knock the valve off of the cylinder. It takes off like a rocket. This is not due to the gases pushing against the air. The cylinder would do the same thing in the vacuum of outer space. The cylinder moves because the pressure against the non-valve end is greater than the pressure at the valve end, where there is now nothing to push against.

The barrel (and slide) recoils backward normal firing because there is more force in the rearward direction. The forward force is only applied to the barrel through the friction of the bullet in the barrel. Imagine a precisely fitting bullet with a gastight and frictionless fit. You can see that there would be virtually no force against the barrel in the forward direction. Now increase the friction of the bullet and barrel a little. The barrel will be dragged forward a little and the recoil will be reduced a little. The bullet will also be slowed down a little. As you increase the friction, the forward force on the barrel increases, the recoil decreases, and the bullet slows even more. Increase the friction enough, and the bullet stops, the barrel tries to move forward as much as it tries to move backward and goes nowhere.

RJ357
August 18, 2004, 07:34 PM
If you use an independent means of preventing the bullet from moving forward, like a rod extending into the barrel and attached to the wall, you will find a rather large amount of recoil, as you might imagine. What's important above with the immobilized bullet, is that the bullet is being held in place by the barrel, or something attached to the barrel.

It is not the forward movement of the bullet that's important, but the fact that is is free to move in relation to the barrel.

baker
August 18, 2004, 08:06 PM
Don't think so. Rocket engines got pressure out the wazoo, in all directions, inside. But the thrust is only in the direction opposite the outgoing gas jet.

The "jet" of hot gases propels the slide backwards, opposite the thrust of the jet. It is "directed" out of the barrel in one direction, and moving the slide backward is the equal and opposite reaction.

Also, the mass of the bullet is contained in the gun, and pushing it out will cause recoil and slide movement.

In the vacuum of space, it is the lost mass of the rapidly burning fuel that propels a rocket forward.

The "bullet pulled by a wire" analogy isn't applicable.

Think both/and, instead of either/or for causing the slide to move.

RJ357
August 18, 2004, 08:21 PM
In the vacuum of space, it is the lost mass of the rapidly burning fuel that propels a rocket forward.

Incorrect.
The pressure of the gases against the front of the rocket motor is what pushes it forward. There is a lack of opposing force in the rear of the motor where it is open.

1911Tuner
August 18, 2004, 08:22 PM
Jim Watson said:

In firing, pressure drives the bullet forward so the same pressure pushes the slide rearward to balance the momentum. Cause and effect. Can't separate them.

Precisely!
_______________

RJ357 said:
When the bullet is immobilized in the barrel, the forward and rearward forces are equal and opposite and cancel. There is no net force in either direction.

And:
While it is true that the bullet NEEDS to move forward in order for recoil to exist, that is NOT the direct cause of the recoil.

Exactly! The "Thrust Vector" pushing equally in both directions is the cause of bullet AND slide movement...Recoil!
________________

My theory...and mine alone...is split between these two questions:

Does the barrel push the slide through the locking lugs and hood...or
does the thrust exerted on the breechface move the slide, causing the slide to pull the barrel along with it?

AND...If it's due to the barrel pushing the slide, does it occur at the interface between locking lugs on the barrel and in the slide...or is it a function of the expanded case in the chamber exerting the force against the breechface and pulling the barrel along with it (the expanded case)
...or is it a combination of the two. I lean toward the theory of the barrel pushing the slide, with the resulting momentum imparted to the slide causing it to continue after the barrel has unlocked. Why? Look no further than the short gas piston of the little M-1 Carbine. A very short, quick movement carries the slide and bolt assembly through the entire cycle...
Momentum. Ditto for the M-14 rifle, though the piston moves farther than in the War Baby.

This one's rollin'! More theories! Make me doubt mine!


EDIT to Add:

baker said:

Think both/and, instead of either/or for causing the slide to move.

Hmmmm... I think I like that one too. Nothing is everything, but everything is something.

Good point!

R.H. Lee
August 18, 2004, 08:33 PM
ACK! Yer givin' me a headache.

For every action, there is an equal and opposite reaction. The bullet leaves the case due to expanding gasses, and heads down the bore. The case, which is expanded inside the chamber, moves backwards (the opposite way), pushing against the breechface, taking the slide along with it. By the time the case has contracted, it has already dumped it's energy into the slide.

RJ357
August 18, 2004, 08:51 PM
Does the barrel push the slide through the locking lugs and hood...or
does the thrust exerted on the breechface move the slide, causing the slide to pull the barrel along with it?

AND...If it's due to the barrel pushing the slide, does it occur at the interface between locking lugs on the barrel and in the slide...or is it a function of the expanded case in the chamber exerting the force against the breechface and pulling the barrel along with it (the expanded case)
...or is it a combination of the two. There would be a combination of effects. The force is back against the breechface through the case head. It is also back against the barrel through the friction of the case walls and chamber. And it is also forward against the barrel through the friction between bullet and bore. I cannot say, though, how much each contributes. The case friction and bullet friction are in opposite directions with a net force in one or the other direction. I am going to guess that the case wall friction is greater, due to the pressure being applied outward against it. This outward radial pressure is not present in the bullet except through an attempted mushrooming of the bullet base. But again, just a guess.
I lean toward the theory of the barrel pushing the slide, with the resulting momentum imparted to the slide causing it to continue after the barrel has unlocked. Why? Look no further than the short gas piston of the little M-1 Carbine. A very short, quick movement carries the slide and bolt assembly through the entire cycle... Even if the slide and barrel received equal force impulses (rearward), the barrel would attempt to accelerate faster than the slide because of lower mass. That would add support to the "barrel pushing the slide theory".

baker
August 18, 2004, 08:59 PM
Incorrect.
The pressure of the gases against the front of the rocket motor is what pushes it forward. There is a lack of opposing force in the rear of the motor where it is open.

OK, I could be wrong, but it WAS what I was taught in public school. :) (That the mass of the fuel leaving the rocket at a high rate of speed causes an equal and opposite reaction, propelling the rocket forward, especially in space, where there are no other gases to push against.)

Actually, I still think I'm right :)

http://science.howstuffworks.com/rocket1.htm

"A rocket engine is throwing mass in one direction and benefiting from the reaction that occurs in the other direction as a result."

See the link. It actually uses a shotgun as an example

RJ357
August 18, 2004, 09:41 PM
"A rocket engine is throwing mass in one direction and benefiting from the reaction that occurs in the other direction as a result."

See the link. It actually uses a shotgun as an example The reason I don't like to explain it that way is because it expresses it in the form of a law but it really doesn't explain why. In the case of the shotgun example, the question still remains as to why the shotgun recoils. If you look carefully at what is happening inside the chamber, you will find one single thing that explains why the shotgun moves rearward: pressure against the breechface.

You are quite correct about action and reaction.

(Just edited this in)

If you look even more closely, at the molecular level, what you will see are gas molecules transferring energy (momentum) to the molecules of the breechface by collision. And it is this alone that produces the force.

Grump
August 18, 2004, 09:43 PM
As long as the barrel and slide are locked up, they are one unit for the sake of recoil. Just like a muzzleloading rifle barrel. You *can* unlock them while the bullet is in the barrel and pressure is way up, but you can't do it using a tilting-link mechanism like a pistol. The inertia of getting the parts moving is too slow.

The "stretch forward" thrust vector to the separate barrel cannot be the sum total average chamber pressure at bullet base at any instant, because the pressure is being released in the direction of bullet travel. I'm sure we're looking at bullet drag, maybe plus a factor for its inertial resistance to acceleration. Intuitively, somewhere between the middle and the last third of any instantaneous powder chamber volume (breechface to base of bullet), there may even be an area where the gas pressure starts pulling the barrel back--there are gas dynamics going on, not a static situation. For sure, a major component of barrel recoil is caused by the slide pulling it back.

That ain't no stinkin' equal force vector.Pressure stays the same and all that, the bullet will go forward, but allowing both the barrel and the slide to recoil together without any resistance to the barrel (the link connected to the frame),
Remember, the barrel and slide are connected by the locking lugs.
Flawed theory. The thrust works equally in all directions. If the bullet and slide/barrel assembly were of equal mass, they would be propelled at the same rate of acceleration in opposite directions.
I don't see what you're pointing out as a flaw. I've fired a Luger "cannon" (top end) without its frame, and the rear/breechface part of the assembly is much nearer to the same mass as the barrel, compared to a .45 barrel/slide assembly's vastly different masses. It recoils as a unit, and any forward thrust vector to the barrel is greatly overcome by the breech end pulling the whole shebang back in recoil.

Pressure is in the powder area an omnidirectional force, work is mass being moved, and thrust is a directional force caused by Newton's law of acceleration??. We may be playing too fast and loose with terms, and missing each others' points...

Bum barrels split longways, not in an annular ring of failure. The forward "stretch" force on a barrel cannot be the same as radial force, because the bullet is releasing the pressure with a relatively small friction drag in the forward direction.

We may be agreeing more than we think...

sm
August 18, 2004, 09:56 PM
Does the barrel push the slide through the locking lugs and hood...or
does the thrust exerted on the breechface move the slide, causing the slide to pull the barrel along with it?- Tuner

My .02
Thrust exerted on Breechface due to

... function of the expanded case in the chamber exerting the force against the breechface and- Tuner

In my thinking , the opposite and equal travel of gases along the same plane. It would seem to me with gases going down bbl - the opposite being gases against breechface - path of least resistance if you will.

P95Carry
August 18, 2004, 09:57 PM
In firing, pressure drives the bullet forward so the same pressure pushes the slide rearward to balance the momentum. Cause and effect. Can't separate them. Just as Jim says. Agreed.

Think also of a sprinter on starting blocks (the analogy to a breech face) .. at ''the gun'' he applies thrust against the blocks ... in order to accelerate forward and get into running mode. His foot pressure is totally comparable with rearward gas pressure vector during the time bullet is accelerated down barrel.

It matters not that we are talking about a gas under pressure .. this is a force, held in control briefly by the resistive inertia of the barrel/slide system... which takes time to react ... time enough for bullet to exit.

Equal and opposites .. no case to be answered!:)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Oh just to add ... of course, gas pressure is applying force in all directions ... but if chamber/ barrel/case head can withstand pressured without rupturing then we have ''confinement'' .. and thus all forces act and are contained within the barrel's long axis... the bolt face remaining as the ''starting block).

As buller leaves muzzle ... gases now have an 'escape route'' ... the easy option .. and so rapidly cease to have any rearward thrust remaining. The obstruction (bullet) ... is gorn!

RJ357
August 18, 2004, 10:15 PM
It matters not that we are talking about a gas under pressure .. this is a force Force on breechface is equal to area of breechface (square inches) multiplied by pressure of gas (lbs / square inch).

Tamara
August 18, 2004, 10:20 PM
'Nother thought experiment:

Does a .45 blank at least partially cycle the slide despite the total absence of a bullet? Will a 9mm blank cycle a 9mm 1911 with a light enough recoil spring, again, despite the lack of a projo engaging the rifling? ;)

(Reverse the thought experiment: Would a caseless delayed blowback gun work?)

R.H. Lee
August 18, 2004, 10:26 PM
Does a .45 blank at least partially cycle the slide despite the total absence of a bullet?

I'll stick my neck out and say I don't think so. No bullet means no mass going down the bore, so there is no opposite reaction.

But then I'm no physics professor, either.

RJ357
August 18, 2004, 10:26 PM
1911Tuner -

Are you asking if the action of the 1911 in particular is responsible for the lack of recoil with a frozen bullet? In other words, it's the fact that the barrel and slide are locked together that's responsible?

(We were supposed to wait for Jim Keenan to reply, weren't we?)
(sorry)

RJ357
August 18, 2004, 10:32 PM
Does a .45 blank at least partially cycle the slide despite the total absence of a bullet? Movie guns require a partial obstruction in the barrel to cycle with blanks. The absense of the bullet results in a very low pressure impulse.Would a caseless delayed blowback gun work?) I would say yes. Almost all of the slides movement is from momentum. The cause of the movement is very short, and almost gone by the time the slide unlocks.

sm
August 18, 2004, 10:36 PM
Tamara -

Would you explain your post a bit more in detail please. :)

I have used the .45 shotshells and they did in fact cycle 1911s. I have used the primer only cases with Wax bullets and have had these cycle . The Speer Rubber did not feed at first very well , I cured that ...still these did not cycle . Must have been the "crimp" affecting the gases?

Tamara is this similar to what you refer to?
Anyone else?

Am in the ballpark ?

baker
August 18, 2004, 10:38 PM
RJ357 said:
If you look even more closely, at the molecular level, what you will see are gas molecules transferring energy (momentum) to the molecules of the breechface by collision. And it is this alone that produces the force.

I respectfully disagree, of course the gas molecules are transferring lots of energy to the breechface and forcing it back, BUT, if there were no mass leaving the gun, the effect would be reduced.

If 230 grains leaves the gun at 850 fps, there IS an equal, opposite force upon the gun. If you stood on rollerskates and threw an object, you would move backwards with the same energy exerted upon your mass, minus friction.

Expanding gas alone is not the whole equation.

P95Carry
August 18, 2004, 10:48 PM
The only mass a blank round has to work against - is the density of the atmosphere .... not enough to create much of a vector rearward.

Contain those expanding gasses by obstructing it's discharge route - even partially, and this simulates to a degree the obstructive effect of a bullet.

Steve ..... if those .45's were shotshells then the BB count (load) will still act as an ''obstruction'' - resistance mass.... or if you like a mass that needs accelerated ... even if in a wad. Still equal and opposite will apply.

RJ357
August 18, 2004, 10:53 PM
I respectfully disagree, of course the gas molecules are transferring lots of energy to the breechface and forcing it back, BUT, if there were no mass leaving the gun, the effect would be reduced.
The effect on the breechface would not be reduced. If the pressure remains, so will the force. What will change is the movement of the barrel (and slide). If there were no mass leaving the gun, it would have to be because the bullet was frozen in the barrel. There would then be an equal force against the base of the bullet (and hence the barrel) in the opposite direction. The pressure and force against the breechface remains.

In fact, a release of gas would result in a decrease in breechface pressure.

middy
August 18, 2004, 11:05 PM
Keenen is right.

Kuhnhausen says it is pressure against the breechface that causes the slide to move. Wrong.

It's all in the barrel.

When the powder ignites, the pressure is in all directions, essentially fusing the casing and the barrel as the soft brass is pushed into the steel of the chamber. It can't slide out of the chamber and exert pressure against the breechface. If the bullet is attached to the barrel by rod and set screw, the cartridge and barrel are now basically just a pipe bomb without enough powder to blow. (Incidentally, I'm quite suprised this experiment doesn't blow the case every time.)

The slide moves because it is locked to the barrel initially, not because of pressure against the breechface.

The barrel moves because if the bullet is free to move out of the barrel the same force is applied against the barrel/casing in the opposite direction.

OK, actually, Keenen is only mostly right, it's not just the mass of the bullet, it's also the "rocket effect" of the burning powder (I think). Now it's like a pipe bomb with a loose plug in one end. Set it off and the pipe and the plug will go flying in opposite directions (assuming you don't have an overcharge which would fragment the whole thing before the plug has time to get out of the way). The lighter plug (the bullet) will, of course, fly faster.

Edited to add:

But even without a plug, imagine a pipe bomb with one end open... it's still going to go flying. Like a rocket. (Hey that is a rocket!)

sm
August 18, 2004, 11:06 PM
Tamara

Chris

I can understand the shotshells being mass or obstruction. I don't know the exact "weight" of that payload . I'm trying to keep the weight - for sake of this discussion at 230 gr .

The Speer Rubber bullets we just stuck in. The Wax ones were from a block of paraffin , so I would think more resistance becasue of more "crimp" is the rason these cycled. ???

Hey - I'm learning. Some stuff I kinda understand but don't know why I do. It is like I pass up some steps. I jsut kinda see it in my mind - I never took physics ....

P95Carry
August 18, 2004, 11:17 PM
middy -

Sure cases expand but - not IMO with enough frictional ''grip'' to cling onto the chamber walls! So I beg to differ.... the case WILL move back to impact the bolt. A ''component'' might be chamber ''grip'' but not much to matter.

Consider the revo --- the reason the recoil shield is there .... it prevents further rearward movement of a case ... remember too - the case ''sets back'' such that a smallish firing pin ''dimple'' becomes a deeper depression .. due to set back against a firing pin that has not had time to drop back! The primer tries to escape the pocket but is whacked by the pin .. again.... and will rarely if ever by other than flush with case head .. so proving set back.

Sorry - the force (yeah ... pressure over area) ... IS exerted on bolt ... has to be. Pressures in these realms will overcome any ''case grip'' in a chamber.!

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Steve ..... a 230 grn ''equivalent'' will be fine ... leaving aside bullet/barrel friction .. this'd equate well OK to a bullet mass.

Wax bullets? ..... well, if crimp good then certainly some useful opposite reaction but - if mass not there then it'll be a diminished rearward force ... has to be.

RJ357
August 18, 2004, 11:21 PM
The law of equal and opposite reaction is important in that it describes the relationship between the two actions.
1) that they are equal
2) that they are opposite

But it does not explain why.
Just as the law of gravity describes how objects fall and in what direction, but does not explain why.

Kinetic forces cannot act over distance. The interacting objects must be in physical contact. It is not a case of radiant energy like light, or forces involving fields like gravity or magnetism. The only thing that matters at the breechface is the pressure, as it is the only thing in contact with it. The actions some distance away may alter the pressure, but it is only the pressure that determines the force.
Whether the breechface (and anything attached to it) moves or not depends on what other forces are acting on the system. If the breechface force is the greater, then it will move.

I hate to make it sound complicated, but it isn't, really. If you look at everything discussed with nothing more in mind than the pressure in just the two directions, it explains everything.

Tamara
August 18, 2004, 11:26 PM
Kuhnhausen says it is pressure against the breechface that causes the slide to move. Wrong.

It's all in the barrel.

When the powder ignites, the pressure is in all directions, essentially fusing the casing and the barrel as the soft brass is pushed into the steel of the chamber.

So, does a PPK cycle this way, too? Or does .380 brass have a lower coefficient of friction than .45 brass? ;)

How does the .45 casing know whether it's in a 1911 (and supposed to drag on the chamber walls) or in a Grease Gun (and supposed to shove on the bolt face)? That's some durned smart brass...;)

P95Carry
August 18, 2004, 11:39 PM
thing that matters at the breechface is the pressure, as it is the only thing in contact with it RJ, that pressure is being exerted within a now empty case .... which makes that case want to travel out of the chamber rearward. It cannot because of the presence of the bolt face - it is constrained.

So the pressure is ''transmitted'' - via said case....... which desperately wants to exit its confining chamber but cannot.Just as the law of gravity describes how objects fall and in what direction, but does not explain why. Gravity is an acceleration .. it acts on objects with mass. It attempts to accelerate them at 9.81 m/s toward the earth's center .. only something resisting that acceleration will prevent this becoming fact. We stand on ground .. and that applies a counter force to the acceleration such that equilibrium exists.

All good fun eh!:)

Tamara
August 18, 2004, 11:48 PM
In clarification, however, what pushes the breechface back is the case. Why is the case heading back? Because the gasses (and bullet, if any) are moving forward. If there's nothing moving forward, nothing will move back. (There needs to be an action for there to be an equal and opposite reaction...)

I'd still need to watch the blocked bore test with my own eyes (and somebody else's gun... :uhoh: ;) )

RJ357
August 19, 2004, 12:04 AM
RJ, that pressure is being exerted within a now empty case .... which makes that case want to travel out of the chamber rearward. It cannot because of the presence of the bolt face - it is constrained.

So the pressure is ''transmitted'' - via said case....... which desperately wants to exit its confining chamber but cannot. You are correct. I ignored the case to simplify, since it is the same amount of force in the same direction.Gravity is an acceleration .. it acts on objects with mass. It attempts to accelerate them at 9.81 m/s toward the earth's center .. only something resisting that acceleration will prevent this becoming fact. We stand on ground .. and that applies a counter force to the acceleration such that equilibrium exists. Also correct. However, it is not attempting to accelerate objects, it is accelerating objects. The force that you feel standing on the ground is the result. If allowed to move freely, you will feel no force, zero G.
Part of Einstein's general theory of relativity concerned this equivalence of gravity and acceleration.
Still doesn't explain why, though. All good fun eh! Excellent fun!

RJ357
August 19, 2004, 12:11 AM
If there's nothing moving forward, nothing will move back. (There needs to be an action for there to be an equal and opposite reaction...) Aha, but what if the bullet is attached to wall with a good strong rod? Will the gun move back now? What is the action?

P95Carry
August 19, 2004, 12:17 AM
''Hey Doc .... my brain hurts!!'' :D :D

JohnKSa
August 19, 2004, 12:41 AM
Pressure does not cause recoil.

If nothing escapes the system then there can be tremendous pressure and there will still be zero recoil--zero movement for that matter.

Recoil is proportional to the mass velocity product of whatever escapes the system and in the opposite direction of the vector of the escaping material.

If no mass escapes then the product (mass times velocity) is zero. That means that recoil is zero as well.

Rockets move because they eject a lot of mass at a tremendous velocity out the back of the rocket motor--not because of the pressure inside the motor pushing against the rocket. Ion engines generate virtually no pressure and yet can attain tremendous velocities because the ions are ejected at very high speeds.

Blanks cause recoil although it is much reduced. They cause recoil because mass (in the form of gas and unburnt powder) escape through the muzzle. Restricting the muzzle increases the velocity of the escaping gas and therefore increases the recoil since it is proportional to the mass velocity product of the escaping gas. Just like reducing the size of the hole in the end of a hose with your thumb increases the velocity of the escaping water.

If you lock the bullet in the barrel by fastening it to the barrel then there will be no recoil because there is no motion. If gas vents then there will be recoil in the opposite direction that the gas is vents.

If you lock the bullet in the barrel by putting a rod down the barrel and fastening the rod to a wall, then there will be recoil-like motion because you have turned the gun into the projectile. The wall is now the breech and the gun is the "bullet". It's not recoil though, the recoil force now goes into the rod and will damage the rod or the wall if sufficient force is applied.

Locking the bullet in a straight blowback gun is similar to putting a rod down the barrel and bracing it against a wall. You make the barrel the breech and the slide the projectile. There's movement of the slide in the rearward direction, but that's not recoil in this case. The recoil will be in the FORWARD direction as the barrel recoils forward in proportion to the velocity mass product of the slide's rearward motion.

Tamara
August 19, 2004, 12:47 AM
All true.

But what causes the slide to move is pressure exerted by the recoiling brass against the breechfrace.

The brass is recoiling in that direction because a projectile and a bunch of gas just went off in the other direction. Newton tells the brass to get moving, so it does, shoving the breechface out of its way and hopping politely out of the ejection port (after banging its little head on the ejector.)

Er, not to put it too anthropomorphically. :uhoh: :o

(In a straight blowback pistol, of course, gas pressure plays a much bigger part in the rearward movement and ejection of the case, since there's no mechanism holding the breech shut until most of the gasses get out of the bore...)

JohnKSa
August 19, 2004, 12:54 AM
But what causes the slide to move is pressure exerted by the recoiling brass against the breechfrace.Not pressure. The brass gets the recoil boot and transfers it to the breech--just like those little desk games--the balls on the strings. When one ball hits the stationary balls, the force is transferred through the motionless balls to the one on the end which then jumps.

Recoil is motion--that has to result from force--which is a function of motion (acceleration). Pressure, in and of itself, does not imply motion and therefore can not, in and of itself cause recoil. Until something moves, there is no recoil.

In fact, the pressure inside the brass case actually slows the recoil velocity by increasing the friction between the chamber wall and the outside of the swelled case.

Tamara
August 19, 2004, 01:04 AM
Pressure, in and of itself, does not imply motion and therefore can not, in and of itself cause recoil. Until something moves, there is no recoil.

If one exerts pressure on a movable object, it tends to move. We're wandering into semantics now.

The breechface has inertia imparted to it and is set in motion by a cartridge case that is recoiling from newtonian forces, as well as having the pressure of expanding gasses acting on it. Since it is not fixed in space, it is trying to move, too, just like the bullet. (Set off the cartridge outside of the gun and watch the brass case depart the premises due to the rapidly expanding gasses inside, right?)

RJ357
August 19, 2004, 01:15 AM
Pressure does not cause recoil.

If nothing escapes the system then there can be tremendous pressure and there will still be zero recoil--zero movement for that matter. That is true, however, when recoil does occur, it is the result of force on the breechface through the case head. That force comes from the gas pressure over the area of the rearward surfaces. A force does not manifest itself because of some distant action.
If it is not the gas pressure producing the force, then exactly what is?

JohnKSa
August 19, 2004, 01:15 AM
If one exerts pressure on a movable object, it tends to move. We're wandering into semantics now.Exactly--semantics--you really meant to say that when you apply FORCE to a movable object it tends to move. ;)

Seriously, it is important. Pressure doesn't imply motion. Air up a tire--it doesn't move. Blow up a balloon--it stays stationary. Fill up an air tank with a compressor--no motion. Scuba tanks stay put even when full.

Recoil results from motion. That means that pressure isn't the answer. You can apply all the pressure you want but until something moves ain't nothin' happenin' recoilwise. It's the motion that generates the recoil. A big part of this is that people are using the word pressure as if it means the same thing as force. Maybe it does to some extent in common usage, but if you mix terms as they are scientifically defined in the attempt to solve a scientific problem the results are going to be confusing.

You can't ignore the semantics of a technical problem and still expect to make sense of the solution.

JohnKSa
August 19, 2004, 01:18 AM
If it is not the gas pressure producing the force, then exactly what is?RJ357,

F=ma

Force = mass times acceleration.

Pressure has no mass. Pressure has no acceleration.

The recoil comes from the MOTION of the MASS of the bullet and other ejecta.

It may come as a shock, but Newton was right... ;)

RJ357
August 19, 2004, 01:26 AM
A big part of this is that people are using the word pressure as if it means the same thing as force. We can use pressure here, because we are talking about specific areas (like a breechface) that the pressure is acting against. If the area is fixed in size, then a particular pressure will always result in a particular force.

The pressure inside an oxygen cylinder results in a force inside, outward against the cylinder walls. The reason the cylinder moves if you put a hole in the side is because you have reduced the force on one side at that spot. The force on the opposite side is greater and so it moves in that direction.

RJ357
August 19, 2004, 01:28 AM
JohnKSa -
Pressure over an area is force. If you have pressure in a chamber, you have force against the sides of the chamber.

Tamara
August 19, 2004, 01:29 AM
Blow up a balloon--it stays stationary.

Once the pressure stabilizes, until then the sides expand away from each other. Like the breechface of an autoloader (and the bullet itself), the balloon walls are not fixed in space.

But, yes, the rearward-moving case exerts a force on the breech, and force and pressure are not the same thing. (Or are they? ;) ) Breechface thrust is usually measured, however, in psi or cup, if I'm not mistaken...

Pressure has no mass. Pressure has no acceleration.

So, what causes the bullet to move forward? :confused:

RJ357
August 19, 2004, 01:30 AM
The recoil comes from the MOTION of the MASS of the bullet and other ejecta.

How??? describe the force on the case head.

RJ357
August 19, 2004, 01:38 AM
Tamara -

Pressure is measured in psi (pounds per square inch) or cup (copper units of pressure).

Force is measured in pounds.

sm
August 19, 2004, 01:41 AM
Tamara - Thank You!
Your post- In clarification, however, what pushes the breechface back is the case....
and follow up posts better said what I was trying to say / what I thought was going on.

JohnKSa - thank you as well.

So what I'm reading is [ correct me please if wrong] even a primed case , no pwdr, no wax , nothing - just a empty primed case will exert force against the breechface from what gases are caused by the primer only.

Tamara
August 19, 2004, 01:41 AM
Correct. PSI and CUP are merely measurements of force over a given area. Which is what pressure is. N'est ce pas?

RJ357
August 19, 2004, 02:30 AM
Tamara - Pressure has no mass. Pressure has no acceleration. So, what causes the bullet to move forward? Hey thanks!, I think that will help make my point.

Maybe it's the same thing that makes the slide and barrel move backward.

And could that be, let's see, oh I don't know, a force due to PRESSURE??

JohnKSa - Force = mass times acceleration.
Force also = pressure times areaThe recoil comes from the MOTION of the MASS of the bullet and other ejecta.And where does the motion of those come from?
It must also be true then, that the bullet's motion comes from the recoil of the slide. No?
And where does the recoil come from in that case?It may come as a shock, but Newton was right... Yes I am familiar with Newton's 3rd law. It is not an explanation, but a description of how objects behave. It does not concern itself with the source or type of force, only with the magnitude and direction of the force vectors.

1911Tuner
August 19, 2004, 05:15 AM
Good gawd! There are some smart folks on this forum...If nothin' else, it lays waste to the notion that we "Gunnies" are a bunch of slobbering,
redneck morons who drive around lookin' for somethin' to kill.

I'm gonna try to simplify a few things and see if it makes sense to anybody but me.

Fact: In order for recoil/slide movement to occur, the BULLET must move.

Fact: The bullet and the slide/barrel assembly START to move at the same time...at the instant of ignition...disregarding the nanosecond required
for the inertial resistance of each component to be overcome. Once the
process has started...movement starts.

Fact: Regardless of how small or large the amount of forward "pull" the bullet exerts on the barrel during passage, it still exists, and can't be discounted.

Fact: No matter how small or large the effect that the case has on the greater slide and barrel mass during gas expansion...it exists and can't be discounted. EVERYthing means SOMEthing...

So far, most of the discussion has been concentrated on the bullet and the
slide/barrel assembly acceleration, and the lowly expendable component...
the brass case...has largely been ignored.

Here's a little something thrown in that may require close consideration:

The brass case is also a projectile during the firing process. Its acceleration
is contained by the breechface...but it's still a projectile.

HYPOTHETICALLY...obtain a barrel with an extremely tight chamber...one that would require as much force to chamber a cartridge as the bullet passing through the barrel. There is no slide in this hypothetical experiment...only the barrel and the cartridge. Suspend the loaded barrel
and heat the primer to the ignition point. Which projectile will be accelerated faster...the heavy one, or the lighter one? In this, the heavier
bullet has become the recoiling component...the slide... and the case has become the bullet...no?

The vector is the force of the expanding gas that is pushing in opposite directions on two points of resistance..the heavier of which tends to resist that force vector to a greater degree than the lighter one, and the barrel will "recoil" FORWARD rather than backward as the "bullet" exits the chamber end.

Note to Grump: Yep...I think that we may be getting close to a balanced vector too...We were just approaching it from different directions.

Okay...Everybody take two Excedrin and think about it a little more.:D

Fred Fuller
August 19, 2004, 07:14 AM
Grumble grumble...

Heads in theoretical clouds, trip over rake.

Not only 'nother thread, but in a completely different part of the forum...

http://www.thehighroad.org/showthread.php?s=&postid=1190671#post1190671

Somebody say something about herding cats?

:^)

lpl/nc

1911Tuner
August 19, 2004, 07:21 AM
Howdy Lee!


Nahhh...Jim's just a "Low Profile" kinda gent, and didn't wanna get tangled up in the ragin' debate on this one. I'll move the other thread to this forum
in a few. Had to let the Collies do their mornin' constitutional....and
they do a right smart job of herdin' the cats around here. It's a sight, I tell ya! Pore ol' cats don't know whether to stand still, shoot marbles, or go for their guns.:D

middy
August 19, 2004, 07:24 AM
OK. Scrap my old hypothesis. :D There is normally pressure on the breechface.

How about this.

Since the bullet is attached to the barrel, recoil can't occur, because just as much pressure is being exerted forward against the bullet/barrel as there is backward against the breechface. The locking lugs are absorbing all that energy, I guess. Normally the barrel is free to move backward with the slide, perhaps only overcoming a bit of friction against the bullet at the very beginning of its movement.

So simple, now that I think about it. :banghead:

Of course, I could be completely wrong again. ;)

1911Tuner
August 19, 2004, 07:27 AM
middy said:

Of course, I could be completely wrong again.

Take two Excedrin...This one's a long ways from over.:D

middy
August 19, 2004, 07:42 AM
I think I'm right with this last one, Tuner.

But I'd like to hear someone prove me wrong. :)

1911Tuner
August 19, 2004, 08:13 AM
Middy said:

I think I'm right with this last one, Tuner.

FWIW, I do too.
________________

But I'd like to hear someone prove me wrong.

Aye! There's the rub. Proving a theory requires experimentation
...sometimes a lot of it, and from several different approaches in order to cover all the angles. That runs into time and money. Until a theory is PROVEN right OR wrong...it's still just a theory.

As the late, great Yogi Berra put it: (so simply)

"In theory...theory and practice are the same. In practice...they ain't."

Cheers all! Be back this afternoon...

Tuner

Tamara
August 19, 2004, 08:40 AM
The brass case is also a projectile during the firing process. Its acceleration
is contained by the breechface...but it's still a projectile.

We were just talkin' about that before you got back. Check the five or six posts before yours. :cool:

The breechface has inertia imparted to it and is set in motion by a cartridge case that is recoiling from newtonian forces, as well as having the pressure of expanding gasses acting on it. Since it is not fixed in space, it is trying to move, too, just like the bullet. (Set off the cartridge outside of the gun and watch the brass case depart the premises due to the rapidly expanding gasses inside, right?)

The brass is recoiling in that direction because a projectile and a bunch of gas just went off in the other direction. Newton tells the brass to get moving, so it does, shoving the breechface out of its way and hopping politely out of the ejection port (after banging its little head on the ejector.)

1911Tuner
August 19, 2004, 09:04 AM
Howdy Tam. You said:

We were just talkin' about that before you got back. Check the five or six posts before yours.

Yeppers....My post was mainly a recapped, condensed restart.
Kinda like startin' over from point B...:cool:

In agreement with it too...but my pore ol' punkin' head is bangin' on me
and I gotta go see MamaTuner to mow for her.

Later on!

Tuner

Brian Williams
August 19, 2004, 09:15 AM
A clear analysis of any situation is often mistaken for pessimism, altruism, or just being a Smart A$$:rolleyes:

Get a Glock:D :D :D

Does a Glock or any type of locked breech, albeit with a barrel hood, have the same lock up thrust vectoring as the 1911



Back to a question of does the barrel push back on the slide by way of the lugs or does the pressure against the breechface cause the slide to pull the barrel back.

Test to show that would be to get a cut away slide with a slot in the top to show the recoil lugs and have a few barrels with varying fits of the lugs, i.e. sloppy or extremely tight and with a high speed vid record the firing.

Now who has a 1911 we can cut up????
Who has the vid cam???




My take is the brass is not a projectile, but a seal and it takes a force from the gas pressure and directs it to the breech face and like a rocket it forces the slide and the barrel back.





You have to be smart to be a SmartA$$

BigG
August 19, 2004, 10:42 AM
Pressure in and of itself is inert. Think of an aerosol can. What causes movement is when something is moveable, the pressure will act on it and whatever else is containing it but first something has to move or the pressure stays contained and is inert.

sm
August 19, 2004, 11:34 AM
This thread is like "the hurrier I go - the behinder I get".

Okay I may not have had Physics, I have been exposed to the Laws in other subjcts ...and dropped stuff on my foot tho'. :p

Here is where I am stuck. I'm still back at the empty case with a live primer only stage.

I still think there is a correlation to case head hitting the breech to get this whole 'movement " thingy started.

I thought the gases that resulted from the firing of primer were considered "mass" . So this primer only case is chambered , and upon firing gases are released down the bbl and the opposite and equal reaction exerts the case aginst breechface. Granted not a lot , still it happens.

When I used the Speer rubber bullets , more "mass". The weight of rubber , increased pressure of gases because they were more "resticted". The wax bullets had more felt recoil and would cycle. I have no idea of the weight of wax vs rubber bullet, , the open mouth of case was pushed into the warm paraffin to a cetain depth. So MY thinking is a tighter seal / crimp resulted in more resistance for gases to escape. Human feel could not measure this slight difference.

Since I don't know , I'm still stuck at the basic primer fired case. Actions were designed to funtion a certain way, in this case the 1911 style. So have to wonder if the basic design was figured first then metallurgy , springs , links and such built to withstand the loading.

Gotta run to class....back later . I get to tear something up :)

Andrew Wyatt
August 19, 2004, 11:40 AM
seems to me that a 1911 is just a hand held version of this. (http://riv.co.nz/rnza/hist/dgun/)

Those seem to work by straight recoil, and their breechblock is locked for the same duration in the stroke as a 1911.

NMshooter
August 19, 2004, 01:36 PM
This thread needs pictures, vector diagrams especially. Each component gets its own diagram. The bullet, case, barrel, slide, link, etc. Remove the locking lugs from the barrel and pin the barrel into the frame. The slide will still move (with far more force than I want to hold in my hands) even with a fixed barrel.

The locking lugs ensure that the barrel recoils with the slide, keeping the breech locked until gas pressure has dropped to safe levels, then the link cams the barrel down, allowing the lugs to unlock and the slide to continue to retract.

Bore out the rifled portion of the barrel to larger than .451" and the pistol will still cycle. I apologise in advance if I further confused the issue.

Edit: Just read the other thread. Jim does a far better job describing things.

Hand_Rifle_Guy
August 19, 2004, 03:29 PM
Does the barrel push the slide through the locking lugs and hood...or
does the thrust exerted on the breechface move the slide, causing the slide to pull the barrel along with it?

Short answer is both. Adequately covered already by others.

Just to stir up trouble, although I think we've got this covered, and inspired by the whole force/pressure discussion, I shall introduce the concept of recoil-less rifles.

These things allow a lightweight barrel to luanch a 3.5" projectile off of an infantry-man's shoulder, if need-be. Velocity's in the 1000 fps range for all of 'em regardless of bore size.

These things are emphatically NOT a rocket-launcher like a bazooka. They use a fixed cartridge with a case. However, the case is pierced all around, allowing the gasses to escape. These escaping gasses are vented to the rear, countering the recoil generated by accelerating the mass of the projectile. The pressure involved is substantialy less than what's encountered in a standing-breech gun, allowing for MUCH lighter construction, but limiting velocities to aforementioned 1000 fps. But it is the balancing of the high-velocity gasses escaping rearwards to the projectile mass going forwards that allows shoulder-laiunching a shell of significant mass without knocking the "mounting fixture", i.e. our stout soldier, flying. I dunno what the actual psi involved IS, but it's gotta be something powerful enough to loft 105mm HEAT rounds off of light bases, yet low enough to allow for thin-walled, easily man-portable gun components.

Oh, and don't stand behind one.

More monkey-wrenching of the local brain trust: There are rocket launchers that have initial boosters that burn entirely within the launch tube, the Stinger being one. This kicks the projectile out of the launch tube fast enough to allow for ignition of the longer-burning primary drive rocket at a safer distance from the launcher. This is a similar effect to, but not the same as the recoil-less rifle, as true rockets exert no recoil on the launching platform. The primary difference is that there is no movement associated with the propellent in the rifle, where-as the pressure containment of the rocket is associated with the vehicle body, not the launch tube.

But don't stand behind one of THESE either! ;)

On a general note, a related-but-different-flavored thread from TFL: How much of recoil is rocket exhaust? (http://www.thefiringline.com/forums/showthread.php?t=101290)

Always stirrin' up trouble, me. ;)

rjk2475
August 19, 2004, 03:34 PM
Tuner said:

Which projectile will be accelerated faster...the heavy one, or the lighter one?


would this be the same as 'which falls faster(accellerates)a feather or a bowling ball(in a vacuum of course)?'

and: "Fact: In order for recoil/slide movement to occur, the BULLET must move."

if we disregard the mechanical setup of the 1911, i am having trouble understanding this. the only analogy to me would be a ballon-much PRESSURE, but no net force. 'tis so?

Bill Z
August 19, 2004, 04:17 PM
Anybody up for Pizza and Beer yet?

1911Tuner
August 19, 2004, 05:52 PM
Hand_Rifle_Guy...I was gonna drag the 106 Recoilless rifle into the fray later on, but since you beat me to it...Why doesn't the 106 Recoilless rifle recoil? Hmmmm? If the projectile traveling through the bore initiates
recoil...why doesn't it apply to that particular boomer?
_____________________

Ron asked:

would this be the same as 'which falls faster(accellerates)a feather or a bowling ball(in a vacuum of course)?

Nope...Gravity provides a constant acceleration, whereas an explosion
between two objects is limited only by the amount of force that it generates...or more exactly, the expansion rate of the propellant. The lighter object will be accelerated at a faster rate...which is why the slide
doesn't move at the same speed as the bullet.
_____________________________

NMShooter wrote:

Bore out the rifled portion of the barrel to larger than .451" and the pistol will still cycle. I apologise in advance if I further confused the issue.

No confusion there, and absolutely correct. There is still a vector of thrust
between breechface and bullet that pushes both in opposite directions.
I'll bet that if you were to open up the bore to provide a slip-fit between
barrel and bullet, that the pistol would "kick" less though...The bullet
won't resist being propelled as much, and hence won't provide quite as
good a launching pad for the force to push from.
___________________________

BillZ...I'm up for the pizza, but I'll hafta pass on the brewski. Had to give it up...Makes me think I'm bulletproof and irresistable to women.:D

RJ357
August 19, 2004, 06:20 PM
OK, you got 40 guys standing around outside. Someone really big takes a gigantic open box and turns it upside down over these guys. They are still standing on the ground and are surrounded by the four walls of the box. They all want to get out and run to walls and start pushing. 10 guys against each wall. They all push equally hard and the walls start to bulge. The box stays in position.

Suddenly, one of the walls breaks loose. the 10 guys on that wall push it outward fairly quickly. The 10 guys on the opposite wall now begin pushing whats left of box along the ground. Not quite as fast as the other guys pushed the wall, because they are pushing three times as much weight.

Does anyone really believe that it wasn't the 10 guys pushing on the box that caused it to move? That it moved for some other reason?

HD
August 19, 2004, 07:14 PM
so near and yet so far ... (and yes i am gonna be mean and not tell you...)
you still haven't 'seen it' yet have you ?( i keep telling you old john was smarter than anyone gives him credit for )
i'll call you later this week...:neener: :p :D

Hand_Rifle_Guy
August 19, 2004, 07:55 PM
Tuner, instant non-expert answer.

Inertia, simplified.: The proprerty of matter that states an object in motion stays in motion, an object (Or mass.) at rest stays at rest. (Simplified doesn't include gravity.)

I'll split the energy involved into three rough chuncks: Projectile thrust, breech thrust, and vent gas.

Action: projectile thrust. Pressure on the projectile base shoves it forward against barrel drag and inertia. Reaction: Breech thrust. Case pressure shoves against the breech and platform inertia, generating recoil, measured as (Potential) movement of mass x velocity.

Action: Breech thrust. Case pressure shoves platform back as recoil to accelerating projectile against inertia. Counter-action: Pressurised gasses are directed rearwards out of platform vents to provide (Counter-reaction.)forward thrust, measured as mass x velocity of the exhaust gasses, against rearward acceleration, countering inertia-generated recoil.

Some of the rear thrust is 3rd law momentum, some of the thrust is from the change in angular velocity of the gasses shoving against the sides of the exhaust vents as they expand as in a rocket nozzle, transferring some of their momentum to the platform, the same principle muzzle brakes operate on. Balancing thrust and angular-momentum transfer of the vented gasses (By controlling vent size, nozzle configuration, and operating pressure.) against the forward acceleration of the projectile against inertia cancles the recoil effect. Recoil is not strictly cancled, but is severly reduced.

Qualifier: I think. ;)

'Zat make any sense?

1911Tuner
August 19, 2004, 08:06 PM
Hand_Rifle_Guy...makes perfect sense to me. In a nutshell,
both the breechface AND the bullet are the launch pads.

Henry! No! I still haven't been able to arrange the camcorder and the Ransom Rest at the same time. But if yo don't help me out a little, I'm gonna strangle ya when ya drop by!:D

Zen! Zen! Zen!

Nighty night all!

HD
August 19, 2004, 08:24 PM
ok , heres a help ... you've got some old time mechanical type engineers among your aquaintances , sit one of them down and ask them why it works ...
(not one of those college edumacated jerks either)
try not to get too upset when you achieve 'enlightenment'...

JohnKSa
August 19, 2004, 08:30 PM
Force is measured in mass times acceleration, not pounds--the units are mass x distance divided by seconds squared.

Pressure is force per area, but dividing by area (distance squared) cancels the distance out of the numerator and means that there is no longer any motion/velocity/acceleration implied.

You can say that pressure is force in one sense, but its presence doesn't imply that there is a NET force until there is motion. That's why tanks with high pressure in them don't move around unless something vents.

You can have all the PRESSURE you want, but until there is motion there is no net force and therefore no recoil.

In other words, until the bullet starts moving all the forces are balanced and there is no net force.

ONCE the bullet starts to move (accelerate) then the forces become unbalanced and there is now a net force acting in the direction of the bullet's motion which accelerates the bullet. The third law says that there will be an equal and opposite force (recoil) acting on the "launcher".

With an easy to move projectile, a light charge and a long barrel it's possible to fire the projectile and have the pressure inside the chamber/barrel be back to atmospheric pressure before the projectile exits the barrel. It won't matter, the gun will still recoil proportional to the mass velocity product of the bullet.

Hand Rifle Guy,

Both forces you describe are recoil forces. One due to the forward motion of the projectile, the other due to the forward motion of the gases.

RJ357
August 19, 2004, 08:31 PM
1911Tuner -

Referring to Jerry Kuhnhausen's balanced thrust vector: Is his position that the bullet drags the barrel forward while the case pushes the slide backward? And that the locking lugs exert enough force that the barrel cannot disengage and drop down? Until the bullet leaves and relieves the pressure on the lugs?

Never mind, I found it.

Dave Sample
August 19, 2004, 09:42 PM
Deleted post. Sorry Cap'n. That observation has nothing to do with the
discussion at hand. Hugs and kisses!:D

Tunerfish

RJ357
August 19, 2004, 10:11 PM
Force is measured in mass times acceleration, not pounds--the units are mass x distance divided by seconds squared.

Pressure is force per area, but dividing by area (distance squared) cancels the distance out of the numerator and means that there is no longer any motion/velocity/acceleration implied.

Force is not measured in pounds???
What is the force of gravity measured in? How about spring force?

Pressure is not divided by area to get force. It is multiplied by area. Force is directly proportional to area and directly proportional to pressure. The area cancels, leaving force in pounds (for example).

P95Carry
August 19, 2004, 10:29 PM
To add for RJ .......

The pressure acting on a surface is defined as the perpendicular force per unit area of surface. The unit of pressure is the Pascal (Pa) ... in metric system. Pounds/sq inch in the imperial system.

Thus ------ Pressure P = F/A Pascals or pounds/sq inch, depending on system being used.

F is the force in Newtons (or pounds) acting at right angles to surface ...... of area A square meters (or inches).

When a force of 20 N acts uniformly over, and perpendicular to, an area of 4 sq meters ..... then the pressure on the are is given by P = 20/4 = 5 Pa. The same will be true if using imperial units but will come out as pounds per sq inch.

This is simplified and care has to be used with units but - this is basically how it is!

JohnKSa
August 19, 2004, 10:31 PM
What is the force of gravity measured in?Pounds is the measure of the effect of the force of gravity on a given mass. It varies with altitude. Slugs is the English unit of measure of mass. Mass does not vary. Pounds is not even a component of the calculation of force.

Pressure is Newtons per area. That is Force divided by Area. That is what I said in my post. Per means division.

Scales are a convenient way to measure effects of certain forces and so spring force is often quoted in pounds even though it is still measured in Newtons like any other force.

In the SI system:

Force = Newtons = kg x m / s x s = mass(kg) x acceleration (m/sxs)

Pressure = Newtons/m x m = kg / m x s x s

RJ357
August 19, 2004, 10:34 PM
P95Carry - I agree completely. What is it in reference to?

( edited ) Never mind, I had misread something.

P95Carry
August 19, 2004, 10:41 PM
RJ .... just quoting from a ref book to support your statement!:)

RJ357
August 19, 2004, 10:58 PM
Basically I agree with all of it. My main objection is to the use of "actions have an equal and opposite reaction" to explain the net force that exists when a bullet is allowed to move. Particularly the way it sounds like there was no force on the breechface until the bullet began to move. I just think it confuses people.

(see my 40 guys analogy above)

JohnKSa
August 19, 2004, 11:06 PM
The "forty guys analogy" is fatally flawed. You have them standing on the ground. That allows them to exert force on the box referenced to an outside plane. The combustion gases are totally enclosed in the cartridge case.

For the analogy to be correct, the forty guys would have to be fully enclosed in the box--not standing on the ground.

RJ357
August 19, 2004, 11:14 PM
That is true, but the analogy wasn't intended to go that far.
Which I should have mentioned.

The guys don't represent gas, only force. The purpose was to show the difference between a bullet (the wall) that wasn't free to move and one that was.

JohnKSa
August 19, 2004, 11:32 PM
But that's the crux of the entire problem!

If they can use the ground to push against and move the box, it changes everything. They have to be inside the box standing on the bottom of the box for the analogy to show what happens in the case we're trying to hash out.

RJ357
August 19, 2004, 11:43 PM
OK, the box has a bottom and they are all running around bumping into walls and each other. The whole box is even jitterring around a little. But no overall movement movement.
They are transferring momentum to the walls, but in an equal amount in all directions.
Now the wall falls off. The momentum transfer is unbalanced and the box moves in the direction opposite the missing wall.
But my claim is that the momentum transfer was there against the "breechface" wall all along and was not just created when the other "bullet" wall fell off.

JohnKSa
August 19, 2004, 11:46 PM
It's the wall moving and the guys escaping from the newly opened end that cause the box to move in the opposite direction.

The other 30 guys can't move the box, they're hitting the walls but they're using the FLOOR to get their momentum that they're transferring to the walls. That means that for every bit of momentum transferred to the walls, they got it from the floor. Until something gets out the box might jitter around a little, but it's not going to move appreciably in any one direction.

RJ357
August 20, 2004, 12:13 AM
We can move the whole thing into deep space and they can now get their momentum from pushing off of each other.

misANTHrope
August 20, 2004, 12:45 AM
Pounds is the measure of the effect of the force of gravity on a given mass. It varies with altitude. Slugs is the English unit of measure of mass. Mass does not vary. Pounds is not even a component of the calculation of force.

A pound is indeed a unit of force, unless all this expensive engineering education I've been paying for is a sham. As you said, the English unit for mass is the slug. From the F=ma law, one pound is defined as one slug multiplied by 32.2 feet per second squared (the acceleration due to Earth's gravity at sea level). See http://scienceworld.wolfram.com/physics/Pound-Force.html . You'll note that the page actually refers to a pound-force, which is the term preferred for technical use. But a pound-force is what your bathroom scale measures when you step on it. Gravity creates a constant acceleration, as opposed to a variable force, dependent upon the mass of an object.

As to the "40 guys in a box" analogy, it is quite valid. Regardless of whether the guys are pushing off from the ground, each other, or being propelled forward by release of intestinal gas, the point is that if they each apply equal force to their point of contact with the box, the net result on the four sides they are pushing against is the same as pressurizing a sealed container. The pressure within a sealed container exerts an equal force on all side of the container. This is why a balloon expands when you blow air into it- initially, the pressure inside and outside is equal. When you blow air in, you pressurize the balloon, and the resulting force against the inside is less than the force exerted by ambient air pressure outside the balloon. Thus the unbalanced force causes the balloon's skin to move outward. But once the skin moves outward, contained volume decreases, and pressure thus decreases, until the force exerted by interior pressure balances the force exerted by ambient pressure and the force exerted due to the balloon's elastic material being stretched.

The point is that pressurized gas exerts a force on the sides of a container, the same way that a bunch of guys would exert force on the side os the theoretical box. If it clarifies things, consider instead that rather than the guys standing on the ground and pushing, that the box is floating stationary in space, and in the center of the box is a rigid sphere or some other object. Six guys, on to each side of the box, brace against the object at the center and they each exert an equal force on the exact center of their side. This is equivalent to pressurizing the box. Now, if one side suddenly detaches from the rest of the box, then that side will accelerate away from the box at a rate proportional to the force exerted. The exact same thing would happen if the box were pressurized and the single wall suddenly detached.

1911Tuner
August 20, 2004, 06:47 AM
Duplicate post on the other thread.
_____________________

Okay....Let's recap Jim Keenan's experiment in which he threaded the muzzle end of a barrel and inserted a rod to block bullet movement. A
set screw was threaded into the muzzle, positively blocking any chance of
bullet movement.

We learned two things from this.

One is that the 1911 pistol is far stronger than many of us imagined.

Two is that if the bullet doesn't move, the slide won't move. This
SEEMS to fly in Kuhnhausen's face on his "Balanced Thrust Vector"
theory of recoil, in which he appears to state that the bullet exits and
THEN the slide recoils...which is wrong. If the bullet is gone BEFORE the slide moves...the slide won't move. There is no resistance(the bullet) to the pressure to act against the slide and cause it to move. No launching pad, if you will.

I submit that because the barrel was pushed forward...and because the
slide and barrel were mechanically connected...the slide COULDN'T
move in the opposite direction. The barrel was keeping it static via the locking lugs. it would be the same as two cars linked together by a chain
and pulling in opposite directions. Assuming equal vehicle weight, power,
gear ratios/torque multiplication, and equal traction...neither one CAN move...until something breaks to make the balanced vector UN-equal.

I propose another experiment. I'll remove the locking lugs from a USGI
Colt barrel and mail it to Jim. Hopefully. he still has the rod and screw,
so that all he needs to do is thread the barrel and go. I realize that the gun will then be blowback operated, but the point is this:

If the mechanical connection between the barrel and slide is broken,
the pressure will be free to pursue the path of least resistance, and the slide will move...probably violently. I suggest a strong recoil spring and a shock buffer. I'll include a buffer with the barrel.

misANTHrope
August 20, 2004, 08:07 AM
I propose another experiment. I'll remove the locking lugs from a USGI
Colt barrel and mail it to Jim. Hopefully. he still has the rod and screw,
so that all he needs to do is thread the barrel and go. I realize that the gun will then be blowback operated, but the point is this:

If the mechanical connection between the barrel and slide is broken,
the pressure will be free to pursue the path of least resistance, and the slide will move...probably violently. I suggest a strong recoil spring and a shock buffer. I'll include a buffer with the barrel.

Indeed, this should be the case. If we examine the pistol with the rod in place, we will see that once the powder is ignited and pressurizes the case, the result can be easily split into two force systems. First, the case walls exert a force out radially against the chamber, but since this force is equal in all directions, there will be no tendency for motion unless there is a mechanical failure. In practice, and for the purposes of our discussion, this radial force can be ignored- I bring it up merely to cover all the bases, so to speak. Second, the force resultant from the case pressure will act upon the base of the bullet and the inside of the case head. Whatever gap may exist either between the case and breech face or the bullet nose and the rod will be closed as the bullet and case are force in opposite directions. For our purposes, we'll assume this gap to be negligible.

So the barrel is being pushed forward via the bullet pushing on the rod, and the slide is being pushed rearward via the case. However, the barrel and slide will remain locked together by the lugs, and there is no unbalanced force to the rear to make the slide and barrel cycle rearward together and thus unlock. But without the lugs to hold the two parts together, the slide should indeed recoil rearward, very violently indeed. I definitely wouldn't put anything of value astern of the guinea pig pistol.

The fundamental difference between the pistol with and without the rod is the amounf of force exerted on the barrel in a forward direction. Without the rod in place, the only force is the result of kinetic friction between the bullet and barrel, which is going to be small compared to the force exerted on the bullet and case by the burning powder. But with the rod in place, the force that previously accelerated the bullet to high velocity before it exited the barrel will all be giving the barrel a violent shove forward.

Tamara
August 20, 2004, 08:58 AM
Force is measured in mass times acceleration, not pounds--the units are mass x distance divided by seconds squared.

Happily, this is the first question answered on the Measurements page of the Physics Tutoring Website (http://www.slcc.edu/schools/hum_sci/physics/tutor/2210/measurements/). :)

Pound, as explained by the bright young engineer type posting before me, most certainly is a measurement of force.

NMshooter
August 20, 2004, 06:03 PM
So, now that we have discussed Browning's short recoil system, anyone want to discuss his long recoil system?:neener:

Andrew Wyatt
August 20, 2004, 08:22 PM
SO the short recoil system works like this:

1. primer ignites.

2. pressure rises in case, expanding case

3. projectile starts to move, barrel and case recoil together, pushing on the slide.

4. pressure drops, freeing case from chamber

5. barrel unlocks, slide continues rearward, removes case from chamber and ejects it.

Is that it?

JohnKSa
August 20, 2004, 09:01 PM
pound is indeed a unit of force Pound, as explained by the bright young engineer type posting before me, most certainly is a measurement of force. You are both correct. That was a really stupid mistake on my part... :( That's what I get for posting without thinking through the units carefully--not used to working in the English system.

My point about psi not being force is still correct--when you divide by the area, the resulting units (which are correct in the metric units I posted) no longer imply motion.

I can't exactly recreate my thoughts since I put this in the same post: Pressure is Newtons per area. That is Force divided by Area.kind of like pounds per square inch is force divided by area... :rolleyes: oh well.

sm
August 20, 2004, 09:04 PM
Tamara ,

Thank you for that Physics Tutoring link :)

Good discussion folks - I thank you all.

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