A Physics Primer

[1911Tuner]

In light of the recent dustup on the recoil operated/blowback thread that was closed due to becoming derailed, I'd like to open a new discussion and hope that it'll stay on track and remain civil this time. There were still points to be made and things to be learned.

It was suggested that a solid plug be welded into the barrel of both designs...and that the blowback slide would move, while the locked breech slide would not.

And that's correct on both counts...and there's a very simple reason for it.

Before I go further, let's revisit Newton's 1st Law that dealing with an object at rest and how an outside force must be applied in order to make it move.

The law doesn't really provide enough information. Not only must a force be imposed, but that force must also be great enough to overcome the object's resistance to acceleration, whether frictional, inertial, or mechanically imposed, or...in some instances...all three.

If the compelling force isn't great enough to set the object in motion, the object will stand still. The forces involved must be unbalanced in order to produce motion. That is...the compelling force must be greater than the resistive force.

Welding a plug in the barrel of the locked breech pistol creates a system of balanced forces. Welding a plug into the barrel of a blowback...or unlocked breech pistol...doesn't.

Rather than drawing this out, I'll offer a few examples of a balanced force system and see if anyone can determine why the locked breech slide won't move with a plugged barrel...and why the blowback slide will.

Standing in a bucket, you can't pull upward on the handle and lift yourself off the ground. The forces are balanced.

Lock your hands in front of your chest and pull in opposite directions, and neither arm will move. The higher the compelling force, the higher the resistive force. The forces remain balanced.

Place your palms together in front of your chest and push as hard as you can...and neither arm will move...because the forces remain balanced.

Place a 100 pound weight on the floor and impose 100 pounds of lifting force and the weight won't move. (Use 101 pounds of lifting fore...and it will, because the forces have become unbalanced.)

The simple act of standing on the floor is an example of a balanced force vector.

Another term for all these examples is "A state of equilibrium."

Can anyone apply this to the two plugged barrels and see why one will move, while the other will not?

Remember:

In order for movement to occur, the forces must become unbalanced. Balanced forces don't produce movement. The result of balanced forces is a state of equilibrium.

And:

In a locked breech system, whatever resists the barrel's movement backward resists the slide's movement backward, because they're mechanically connected...while in the unlocked blowback...they're not. This is the big clue.

Get your thinkin' caps on...and let's keep this one in the road.

 

[berettaprofessor]

Having not seen the other thread, you've lost me entirely. But I suggest that if you tried the experiment of placing a plug into the barrel of either, you wouldn't be around after firing to see if the slide would move.

 

[barrow]

hey Tuner.
What stands out to me when i read these discussions is that people seem to have a hard time accepting that the barrel is trying to go forward with the bullet untill the bullet is free of the barrel.

 

[Nom de Forum]

In light of the recent dustup on the recoil operated/blowback thread that was closed due to becoming derailed, I'd like to open a new discussion and hope that it'll stay on track and remain civil this time. There were still points to be made and things to be learned.

It was suggested that a solid plug be welded into the barrel of both designs...and that the blowback slide would move, while the locked breech slide would not.

And that's correct on both counts...and there's a very simple reason for it.

Before I go further, let's revisit Newton's 1st Law that dealing with an object at rest and how an outside force must be applied in order to make it move.

The law doesn't really provide enough information. Not only must a force be imposed, but that force must also be great enough to overcome the object's resistance to acceleration, whether frictional, inertial, or mechanically imposed, or...in some instances...all three.

If the compelling force isn't great enough to set the object in motion, the object will stand still. The forces involved must be unbalanced in order to produce motion. That is...the compelling force must be greater than the resistive force.

Welding a plug in the barrel of the locked breech pistol creates a system of balanced forces. Welding a plug into the barrel of a blowback...or unlocked breech pistol...doesn't.

Rather than drawing this out, I'll offer a few examples of a balanced force system and see if anyone can determine why the locked breech slide won't move with a plugged barrel...and why the blowback slide will.

Standing in a bucket, you can't pull upward on the handle and lift yourself off the ground. The forces are balanced.

Lock your hands in front of your chest and pull in opposite directions, and neither arm will move. The higher the compelling force, the higher the resistive force. The forces remain balanced.

Place your palms together in front of your chest and push as hard as you can...and neither arm will move...because the forces remain balanced.

Place a 100 pound weight on the floor and impose 100 pounds of lifting force and the weight won't move. (Use 101 pounds of lifting fore...and it will, because the forces have become unbalanced.)

The simple act of standing on the floor is an example of a balanced force vector.

Another term for all these examples is "A state of equilibrium."

Can anyone apply this to the two plugged barrels and see why one will move, while the other will not?

Remember:

In order for movement to occur, the forces must become unbalanced. Balanced forces don't produce movement. The result of balanced forces is a state of equilibrium.

And:

In a locked breech system, whatever resists the barrel's movement backward resists the slide's movement backward, because they're mechanically connected...while in the unlocked blowback...they're not. This is the big clue.

Get your thinkin' caps on...and let's keep this one in the road.

I participated in the other thread. Any dust I blew-up was due to the implication that a short recoil system is essentially the same as a delayed blowback. I had recently participated in a thread where one contributor was creating terminology similar to “firing inhibitor flibbitty gibber switch” and that had already put me on edge due to the attempt to change well defined and understood firearms technology.

I agree with what you have written in this O.P. about what would happen in the scenarios given. I would like to add that what is happening in both blowback and short-recoil actions is force overcoming inertia. We do not designate these two very different actions “inertia actions” as it is not sufficiently specific of what is really going on. Neither should we consider a short-recoil action to be essentially the same as a delayed blowback. A delayed blowback in the plugged barrel scenario would result in the slide moving.

 

[Nom de Forum]

Having not seen the other thread, you've lost me entirely. But I suggest that if you tried the experiment of placing a plug into the barrel of either, you wouldn't be around after firing to see if the slide would move.

The blowback action opens with such force that the slide peens, cracks, and/or distorts the frame so much the slide is seized and does not return to battery. I have personally seen an aluminum framed .380 peened from 120gr cast lead loads at standard pressure.

The short-recoil action suffers a blown case head and split barrel just in front of the chamber.

Over the years I have accumulated a collection of uh-ohs from people. One item in it is a 1911 barrel that looks as described above due to a barrel obstruction.

 

[Nom de Forum]

hey Tuner.
What stands out to me when i read these discussions is that people seem to have a hard time accepting that the barrel is trying to go forward with the bullet untill the bullet is free of the barrel.

Anyone doubting the veracity of barrow's post should google "blow forward action".

 

[barrow]

The impact area is the FRONT of the barrel lugs and the REAR of the slide lugs. If the barrel was forced backwards during recoil it would simply follow the slide and there would be no need for locking lugs.

 

[barrow]

When I was a young teenager, I made a (potentially dangerous) peashooter. I used an aluminum arrow shaft pressed into a .38 special case for the barrel. A small charge of black powder would propel a pea through both sides of a cardboard box. A slight overload would propel the barrel out of the gun and I would have to go find it. The pea would be gone as well. Think this would be the same principle.

 

[pendennis]

Anyone doubting the veracity of barrow's post should google "blow forward action".

The concept of blow forward is usually lost on folks, since the force of a bullet (say 150 grains), is miniscule compared to the weight of a pistol. The distance covered, usually 5", or less, happens so quickly that shooters are unaware of the phenomenon.

I was taught in physics, to break every movement down in a given action/reaction scenario.

It's the same in any science, whether chemistry, computers, or biology. The micro studies, which are the foundation of the macro, are most often ignored.

 

[mcmancini]

This sounds like a similar situation to the airplane on a conveyor belt thought experiment: different answers appear due to different implicit assumptions.

I didn't see the original thread, but I'm afraid I don't see how the actions would see different results. I would think that regardless of action type, the high pressure of the burning gun
powder needs to equilibrate with the surroundings, which will result in the breech opening, which will result in slide motion. Perhaps I don't get the original thought experiment.

 

[barrow]

The original thread was entitled Short Recoil Question.

 

[Hurryin' Hoosier]

I guess I'm trying to figure out what your point is.

 

[mcmancini]

I'm confused, is the plug in the muzzle end or the breech end? Seems like both were discussed at some point.

I think a free body diagram would clear things up.

 

[barrow]

I think the thing that everyone agrees with is that if the bullet doesn't move, a blowback action would still function. A short recoil action would not. The argument is why.

 

[Nom de Forum]

I think the thing that everyone agrees with is that if the bullet doesn't move, a blowback action would still function. A short recoil action would not. The argument is why.

In this thread, so far, I have not observed any argument of the validity of the statements in the O.P. In the other thread there were challenges to bets, talk of establishing an escrow account, actual suggestion of an escrow account company, and other hilarious comments! Personally I thought that thread was more of a pie throwing to the face contest than a :banghead:dust up.

 

[RX-79G]

This new thread would have value if it's title was "Autoloading action primer". As a physics thread it is so-so.


In the other thread I responded to every major point with solid counter examples, all of which 1911Tuner ignored, presumably so he wouldn't have to deal with them.

So, here we go again:

All locked breech actions remain locked for some period of time. All unlocked actions are never locked.

All autoloading actions use energy derived from the firing of a cartridge. That isn't a physics problem, just an observation that none of them have motors. How that force is harnessed to open move the action and what sort of pros and cons come with each is why we bother to have terms like "blowback".

Here are all the different major action types for breech-loading autoloaders:
Locked breech recoil. Long recoil ejects the casing when the barrel is moving forward and the breech is locked back, short recoil ejects the casing when the barrel locks in position and the breech continues back. Secondary extraction - the extractor has to pull the casing out of the chamber.

Locked breech inertial unlocking. Used in some Benelli shotguns. Uses a locked breech with extraction provided by residual chamber pressure. Primary extraction.

Locked breech gas unlocking. Gas from the bore is tapped off to move a bolt carrier that angles the breech bolt so that it unlocks from the barrel, then pulls the bolt back to secondarily extract the casing.

Unlocked blowback. Gas pressure formed between breech sealing cartridge casing and bullet provide pneumatic force on breech face that drives it open. Self extracting (primary extraction).

Unlocked blowforward. Gas pressure formed between breech sealing cartridge casing and bullet provide pneumatic force on breech face that drives it open. Self extracting (primary extraction).

Unlocked delayed blowback. Gas pressure formed between breech sealing cartidge casing and bullet provide pneumatic force on breech face that drives it open. Self extracting (primary extraction). Uses a secondary device to decrease the speed of the breech opening without resorting purely to breechface mass or spring pressure. Gas, leverage, rifling leverage and friction delays are most common. The "delay" is not a pause, just a decreased rate of acceleration.


We have these terms so they tell us what to expect out of the firearm. Locked breech actions provide protection against over pressure rounds. The extraction is usually secondary, and the extractor works hard to tug the casing out of the chamber. No matter how much pressure the chamber has or does not have, they generally won't cycle without the bullet moving out of the barrel.

Unlocked "blowback" (or forward) actions require the gas seal of the casing because they use chamber pressure to force the unlocked action open. In the event of an overpressure, they open that much faster. They cycle whether the bullet goes anywhere or not - all they need is chamber pressure.


Let's address this Barrel Friction nonsense. The only gun where barrel friction is actually a factor in the cycle is the FN FiveSeven. The high speed bullet's friction is enough to prevent the light slide/barrel from recoiling. Otherwise, the Browning Auto 5 short recoil shotgun demonstrates that barrel friction in recoil actions doesn't matter - high friction slugs cycle just like low friction buck shot. It doesn't matter what the friction is at 1 inch a minute - that isn't how fast the bullet moves and it isn't the same. Blowforward works because the barrel is a gas tube and bullet and casing are forcing themselves out of either end. If the breech won't go back, the barrel will go forward as the casing shoves its way out.


Here's some more previously ignored examples from the other thread:

If you replaced a Glock's barrel with a magnetic tube that hurled a loose fitting 150 grain slug at 1000fps, the barrel and slide would recoil opposite of this acceleration. The barrel would cam down and stop while the slide's momentum would cause it to continue, extracting anything that happened to be under the extractor hook. In this example, recoil alone caused the gun to function normally. The same barrel installed on a blowback or blowforward gun would cause nothing to happen, despite the slug also heading out the barrel at 1000fps. Recoil did it all.

If you squibbed the barrel of a Glock, blowback and blowforward guns, then fired a high pressure blank in all three, you'd find the Glock wouldn't move at all, and both blow guns would eject their casing. Recoil, known in physics as the equal and opposite reaction to acceleration, didn't power the Glock. Gas pressure acting on the breech didn't power the Glock, either. It only powers a breech that is open to gas pressure action - unlocked breech guns.

Can a blank cycle a recoil operated gun? Sure, as long as the sum total of the mass times velocity of the gas and packing is equal to the minimum bullet momentum that will cycle the gun. Chamber gases have mass, and if they are moving a cotton wad fast enough, they can have significant enough momentum. But most recoil guns won't work this way.

Can a blank cycle a blowback? Similar problem, but now it is a question of chamber pressure being high enough with no bullet sealing the other end of the bore. Make the slide or spring lighter, and it becomes possible to get enough chamber pressure.

Can a blank cycle a gas operated rifle? Like a blowback, the problem is again creating enough pressure in the barrel and gas system despite not having a bullet to seal the other end. Devices are made for this.


What happens if you don't use a casing? Say you loaded a recoil and blowback gun like a blackpowder gun with a loose bullet and no brass. When fired, the gas would leak at the breech of the Glock, but the gun would still cycle. The blowback gun would blow open it's breech immediately, lose all chamber pressure and the bullet would just sit there and the slide would close after only moving a tiny distance. Another fine example of the difference between the pneumatic forces driving a blowback and the recoil forces working in a recoil operated Glock.

What happens if you double load round with too much gunpowder? If it doesn't blow up the barrel, the Glock is going to fire the bullet downrange, cycle the action and eject a spent case. The blowback or delayed blowback gun is going to have the action open faster than normal (more pneumatic pressure) and the casing is going to rupture, blowing brass and hot gas everywhere. That's the primary functional difference between locked actions and unlocked - gas pressure doesn't matter to the locked actions, but it is a major safety problem for unlocked blowback actions.


Summary: You can drive a recoil action with pure recoil, no gunpowder needed. But you do need something accelerating enough to cause an equal and opposite reaction.

You can cycle a blowback gun without any recoil. All you need is enough gas pressure and casing that will seal it. The amount of gas pressure will dictate the speed the action opens, not the momentum of the bullet. Different powders could make the bullet have the same muzzle velocity with completely different slide speeds. This is not possible with a recoil gun - slide velocity is only dictated by muzzle velocity, not bore gas pressure.



It drives me absolutely crazy that a cult of personality can overcome the real definitions of well understood terms and allow someone to argue his own new definitions. These terms all have real world applications. This is not the first time 1911Tuner has substituted his baloney for the facts and gotten away with it for awhile.

 

[Tinman357]

RX 79G. i read the thread. Both of you made valid points. You obviously have a scientific background. I belive the confusion arises from treminology. Tuner has a wealth of knowledge gained by a lifetime of hands on experience. I respect his opinion and greatly value his knowledge. Yours is just as valuable to me.

That being said, knowledge and familiarity with scientific terminolgy is a good thing, but if your audience loses the point from trying to decipher the terminology.

You seem very educated. But in my operational area you would no doubt be just as lost as anybody else that has no time in a military command center.

Ive had some world class intellectuals look at me like some kind of martian when I forget and drop into military speak, loaded with acronyms that aren't used outside of that environment.

For example, me stating that aegis trak 54 vector 243 angels 5 690 knots, sm2 block1 away on intercept. Cheese whiz track on inbound hostile. Hard right to 120 flank. Probably wouldn't mean much to you, but. That phrase wakes me up in a cold sweat.

Tuner and you both have valuable experiance. It would help all of us if the micrometers were put away.

 

[1911Tuner]

Interesting.

So far, barrow is the only one who sees why the plugged, locked breech pistol wouldn't function. Couldn't function. He sees it.

It can be explained in about three sentences.

RX...I see that you're still tryin' to find a loophole. Good luck with that.

But I suggest that if you tried the experiment of placing a plug into the barrel of either, you wouldn't be around after firing to see if the slide would move.

The hypothetical assumed using a blank...but as long as the plug was arranged to touch the bullet with a live round...you'd be wrong.

Some years back, our own Jim K devised a demonstration in an attempt to show that Kuhnhausen's "Balanced Thrust Vector" description was wrong.

He turned a steel rod to fit the bore of a 1911 barrel...then form-turned it to closely match the shape of the bullet nose....then threaded the muzzle for a screw. This, to prevent any bullet movement.

Then he loaded the pistol with GI hardball ammunition and fired it...and nothing happened. After repeated firings, he removed the rod, and fired the gun. If functioned normally.

What Jim didn't understand is that...in his attempt to disprove Jerry's balanced thrust/force vector description...he actually created a balanced force vector...a system that couldn't possibly work because it was a balanced force system...a locked system.

And here's the real shocker. Years before Jim did his mad scientist demo...it was done with a 1903 Springfield rifle using issue ball ammunition...and nothing happened with that one either. I can't remember who did it...but the name Fackler keeps poppin' up.

All motion begins and ends with force. Force makes it move, and force brings it back to a state of equilibrium.

Objects only move if they're forced to move, and the instant that it moves, outside forces that are fighting to stop it are in play.

All action/reaction systems are driven by force forward and force backward. All of them.

And those forces must be unbalanced in order for movement to occur. If the forces are balanced, nothing happens. Stand in a bucket and try to lift yourself by pulling up on the handle. Balanced forces.

I'll toss in another clue.

In the plugged locked breech pistol...if you drill a quarter-inch hole in the center of the plug...the slide will move, even though the "projectile" remains frozen in place.

Why?

 

[1911Tuner]

T'was asked:

"What is the point?"

Partly because...although RX is technically correct in his assessment that a welded plug in the locked breech pistol won't function and the unlocked breech blowback will...he doesn't seem to understand why.

He steadfastly keeps trying to separate recoil from force backward...insisting that they're not the same...or at least that recoil isn't caused by force backward. He keeps looking for that loophole in Newton's 1st and 3rd laws.

And partly because many of the people who were following the other thread probably got lost in the dazzling fireworks display and semantics.

 

[Ash]

You are stating, in effect, that the rearward force of the ignition is balanced by the fact that the forward force (bullet trying to leave the barrel) are equal because there is nowhere else for the energy to leave the system (this assumes, of course, a perfect seal at the breach AND at the bore) not that different than holding in a sneeze. You imply that even the slightest lack of a seal at the bore would mean that the forward pressure would subside first as pressure vents out the bore and the rearward, sealed, gas would generate higher pressure to the rear and so operate the system (unbalanced - there is now more force rearward rather than forward). The reason the system does not work until the bullet leaves the bore is that while the bullet is in the bore, fore and aft forces are balanced and equal. Since the system is never perfectly sealed, the gas escaping where it escapes at a slow enough rate that the force generated does not exceed that required to move the slide, which means that to make the system unbalanced, the rearward forces would not merely require the force rear to be slightly more than the force forward, but would have to increase above the sum of the rearward force and the force required to move the slide (that force being expended to move the slide against the recoil spring). In other words, balancing the system would mean forward force equals rearward force minus the force required to move the slide. One could calculate the force lost through an opening in the bore and as long as that force equaled the amount required to move the slide, the entire system would STILL remain balanced and so closed.

The reason you get bore ruptures or bulges has nothing to do with this discussion as it relates only to the ability of the bore to contain all the forces of the ignition (because there are not merely fore and aft forces, but 360 degrees worth of exerted force in a non-Euclidean way).

The conclusion is that the slide doesn't even start moving rearwards until the bullet has left the action and force at the muzzle is not equal to the force still exerting everywhere else, including but not exclusive to the breach? Were there to be a failure anywhere in the barrel at this point, the slide would begin to move rearward (though how much depends on how big the failure is and this assumes no change in the shape of the barrel that could prevent slide movement due to binding between barrel and slide).

 

[Nom de Forum]

RX 79G. i read the thread. Both of you made valid points. You obviously have a scientific background. I belive the confusion arises from treminology. Tuner has a wealth of knowledge gained by a lifetime of hands on experience. I respect his opinion and greatly value his knowledge. Yours is just as valuable to me.

That being said, knowledge and familiarity with scientific terminolgy is a good thing, but if your audience loses the point from trying to decipher the terminology.

You seem very educated. But in my operational area you would no doubt be just as lost as anybody else that has no time in a military command center.

Ive had some world class intellectuals look at me like some kind of martian when I forget and drop into military speak, loaded with acronyms that aren't used outside of that environment.

For example, me stating that aegis trak 54 vector 243 angels 5 690 knots, sm2 block1 away on intercept. Cheese whiz track on inbound hostile. Hard right to 120 flank. Probably wouldn't mean much to you, but. That phrase wakes me up in a cold sweat.

Tuner and you both have valuable experiance. It would help all of us if the micrometers were put away.

I have no experience in the Navy but I think you just described a Aegis system equipped warship firing a SAM at a target flying at 5,000 feet on an intercept course, ordered your rotary cannon antiaircraft gun to be prepared to fire should the SAM miss, and a right turn to 120 degrees and a speed increase to maximum.

1911Tuner and RX-79G later today I am going to have to go over your posts with a fine toothed comb before replying in detail. Thank you both for taking the time to post comments that exercise the mind.

 

[1911Tuner]

The conclusion is that the slide doesn't even start moving rearwards until the bullet has left the action

No no! If the system is free on both ends to operate...to move...action and reaction begin at the same instant. There may be a tiny delay on the slide starting due to a few thousandths of headspace...but the action and reaction start at the same instant.

And Nom de Forum is getting close to explaining why the slide won't move in the locked breech system with the welded plug.

Close...

1911Tuner and RX-79G later today I am going to have to go over your posts with a fine toothed comb before replying in detail.

I've already said that his assertions as to the welded plug in the locked breech and unlocked/straight blowback are correct. He just doesn't seem to understand why, and he's using the analogy in an attempt to disprove my assertions that they all operate in pretty much the same way and for same reasons. That recoil is nothing more than force backward.

This thread on balanced forces is my attempt to help him see it in spite of his snarky nature.

 

[Ash]

So, you say in a locked-breach system, the slide is moving before the bullet leaves. If that is the case, it WILL unlock because at some point the barrel pivots out of the way. You'd have to plug the barrel AND fix it so that it could not pivot downwards (or rotate, or what ever is what unlocks the barrel and the slide). In that case, it would never unlock and so never open.

The discussion relies on whether or not the slide is put into motion. If the system is closed, the force attempts to go in every direction at the same time. The reaction rearward and the action forward of bullet movement could theoretically be enough to open the action as the slide moves rearward (assuming no recoil spring, as I would imagine it would absorb that rearward energy and so prevent slide movement).

Indeed, if action and reaction are the case, the reaction is only due to the action of the bullet and so a strong enough recoil spring would contain the system were it plugged. Without a recoil spring, the action could open if reaction exceeded that required to move the slide. It would move rearward until the barrel pivoted down (in most recoil systems).

 

[1911Tuner]

So, you say in a locked-breach system, the slide is moving before the bullet leaves.

Sure. Here's proof in this old fluroscope photo taken of a 1911 during the firing phase. The bullet base is about an inch from the muzzle.

Take note of the position of the link and the slide/frame alignment at the back.

Look also at the lugs and how they're engaged horizontally.

Equally interesting is that if you look closely, you can see the bones in the shooter's hand...and that the muzzle has flipped very little, if at all.

Here, the slide appears to have moved roughly .070-.075 inch...and relative to the bullet's position, that's just about right.

 

[Ash]

Right, so plugging the bore closes the system and negates the pressure built up by ignition. The entire system is driven by the bullet and the slide's reaction. The reason the slide does not open is the rearward reaction to the bullet's forward motion is overcome as the bullet contacts the plug and so pulls the slide forward again, assuming the plug were not moved by the impact of the bullet.