Energy Used To Operate An Auto

[MikeIsaj]

The subject came up in a BS session recently and got me thinking (always a dangerous thing). Does anyone know what percentage of a rounds energy is used to operate an auto. I am sure it varies among guns, but is it a consideration. It would sem that the less energy required to operate the mechanism, the more energy would be added to the rounds velocity. After that my head starts to hurt while considering all the possibilities.

Any thoughts?

 

[tater_salad]

as far as an auto pistol, I thought they were all recoil-operated (for the most part), meaning that it's not the expansion of the gasses from the cardridge pushing the slide back like in most rifles with a gas tube, it's the actual force of the explosion. I'm not a physics major, but I can't see too much energy lost from that, anyone else care to chime in

 

[Medusa]

Impulse (mass*velocity) of the leaving bullet must be met with impulse equal in value and direct opposite in direction in order to maintain the equilibrium of whole system by the laws of nature. You guessed it - recoil. As the slide flies back it compresses the spring and it requires force to do so (and depends on the properties of the spring) thus saving some of the energy created by the movement for the returning of the slide to the front back again thus loading new cartridge. Thrown out case takes out the heat created by the powder burning thus minimizing this energy type's role in the whole. And the rest of the energy is carried to the shooter who absorbs it the best way he/she can and it's quite a lot. I've seen some videos where poorly hold weapons do rocket back.

EDIT: I hope it's understandable and I do apologize in advance as english is not my primary language.

 

[BHPshooter]

Tater is correct re: Automatic handguns (with exceptions like the Desert Eagle) do not use the expanding gases to operate the action. They are operated by the recoil impulse of the fired round, so -- considering that you are talking about a locked breech pistol and not a blowback -- no propulsion energy should be lost.

In other words, the action doesn't operate from energy taken from driving the bullet, it takes its energy from recoil. It's a win-win situation.

Wes

 

[MikeIsaj]

Thanks guys. I forgot about that action-reaction thing. Sometimes when you think too hard, the obvious escapes you.

Medusa: No apology needed. You expressed yourself well. Better spelling and grammer than I use sometimes.

 

[Lone_Gunman]

How many foot-pounds of energy does it take to cycle the slide on the average 1911 with standard weight springs?

 

[Peter M. Eick]

When I go out and shoot my big 610 with 40 S&W loads, it feels about the same recoil as when I shoot my 1911 10mm with 10mm loads. I would guess therefore that about 30 to 50% of the recoil energy is being bled off to run the action.

Also, the perception of the recoil has changed a lot. Instead of a kick, it is now a push because you have spread the impulse out over a lot of time and more induvidual actions.

 

[1911Tuner]

Energy

Condensed version of impulse (recoil) energy in a short recoil pistol:

Pressure drives the bullet forward at the same time that it drives the slide rearward. Locking lugs engage and create the locked breech, which keeps the two parts from separating. Energy required to accelerate the bullet drops as the bullet accelerates. Slide has greater mass than the bullet
and barrel therefore conserves greater momentum. Shortly after bullet movement begins, the slide's conserved momentum starts to overcome the mass of bullet and barrel and pulls them rearward with it.

At one-tenth of an inch of rearward slide travel(nominally) the barrel starts the unlocking phase. At some point prior to the beginning of the barrel's unlocking sequence, the bullet exits the muzzle and chamber pressure falls off to nearly zero. Slide continues rearward. At one-quarter inch of travel, the barrel is fully linked down and in bed. Slide continues rearward to complete the recoil phase of the cycle. In other words...The momentum needed to complete the recoil phase is established in the first one-tenth of slide travel...or a few thousandths less. If the bullet is still in the barrel at the beginning of the unlocking phase, chamber pressure is still high and case rupture results. If the bullet exits the barrel before sufficient momentum is established, the slide will short-cycle. If resistance to the slide's rearward movement encounters too much resistance for the momentum to overcome, it will short-cycle. (Too-heavy recoil spring...Physical barrier, etc.)

The recoil spring has very little to do with unlock timing...almost nothing, in fact. It has nothing at all to do with containing chamber pressure. Chamber pressure falls off before the recoil spring has compressed more than one-tenth inch.

So...The amount of energy required to operate a 16-ounce slide with a 16-pound spring is pretty low because it obtains the necessary momentum to complete the cycle in the first one-tenth of travel. Slide weight is about 16 ounces. Slide travel is roughly 2.25 inches. Recoil spring resistance rating is about 16 pounds at full compression...or 16 pounds at 2.25 inches. Figure the load per inch and the amount of energy needed to move a 16-ounce slide,
a 6-ounce barrel and a half-ounce bullet one-tenth of an inch...and add the figures together. Forget bullet frictional resistance because it's being pulled rearward with the barrel as it accelerates.

 

[TMM]

if it takes up any power, i bet it's less than what's lost in the cylender gap on a revo...

~TMM

by the way, the powder BURNS, it DOES NOT explode. if it exploded, the gun would be blown to pieces.

 

[BluesBear]

if it exploded, the gun would be blown to pieces

Not true.
That would depend on the pressures created by the explosion.

A firearm is nothing more than a disposable piston internal combustion engine.
Many internal combustion engines rely on explosions inside the cylinder.

Black powder is classified as a low explosive. It explodes and yet the guns designed to fire it as well as guns proofed for smokless powder do not commonly disintegrate upon firing black powder loads.

 

[JohnKSa]

Pressure drives the bullet forward at the same time that it drives the slide rearward.

Pressure moves the bullet forward, but the slide/barrel won't move until the bullet starts moving. The pressure drives the bullet, but conservation of momentum drives the slide/barrel. Once the bullet exits the barrel then you may have some gases driving the slide/barrel in rocket fashion. Until that point, the only force acting on the slide/barrel is recoil.

Locking lugs engage and create the locked breech, which keeps the two parts from separating.

The locking lugs engaged when the gun went into battery. That locked the slide and barrel together and they will therefore move as a unit, not individually during the early phase of the firing sequence. The case is also part of this unit and therefore any forces against it can't act against the slide without acting on the barrel as well.

Slide has greater mass than the bullet and barrel therefore conserves greater momentum.

The slide and barrel were locked together when the gun went into battery, so any conservation of momentum acts on the unit, not on one or the other. In fact, spreading the momentum forces between the barrel and the slide is exactly the point of JMB's design.

 

[1911Tuner]

Locked?

Ooh! Ooh! John! I beg to differ! The locking lugs aren't locked when the gun goes to battery either, neither...If they were, you couldn't pull the slide back...Kinda like a true locked-breech design...a bolt-action rifle. The locked breech only becomes locked when the pressure starts tryin' to push the slide in the opposite direction of the bullet...tied to the bore through friction, pulling the barrel forward... and the barrel and slide are hooked up via the locking lugs. They engage loosely...unless the barrel is tightly fitted to the slide...(See barrel endplay) but it's still not locked until it goes bang.

Disagree that pressure moves the bullet while only conservation of momentum moves the slide/barrel. Conservation of momentum KEEPS the slide moving once it starts...but something has to get it started....and it ain't bullet acceleration/movement. Why do you suppose that the breechface/boltface is also referred to as the "Thrust Face"? Because there is thrust acting against it. Try grinding the lugs off the bolt on a bolt-action rifle. The rifle won't kick much, but it'll bury the bolt in your cheekbone, I betcha. Blow the case head too. In order for both the bullet and the slide to move, there must be a force acting on both parts...in opposite directions. That force is chamber pressure.

Hypothetically pull the bullet through the barrel at the same rate of acceleration...slide no move. Block the barrel so that the bullet can't move and slide no move because an equilibrium is struck and remains until pressure drops. (The lugs lock and the slide's mass can't overcome the blockage because it keeps constant pressure on the barrel...which is tied to the slide via the lugs.) Block the barrel AND remove the locking lugs, slide move double fast. Why? Pressure drive slide rearward...THEN conservation of momentum is established.

Still doubt? Ask what makes a straight blowback pistol work. The only real difference between the two is that one has locking lugs and the other doesn't. Why would simply adding locking lugs change the physics? Look at a blank firing pistol. There is no bullet to cause recoil...yet the slides cycle.
What do you suppose causes the slide to cycle when there is no bullet?
Ever played with an AR-15/M-16 with a blank-firing device? That's a locked-breech design too...yet when you install a suitable device it functions without a bullet.

Try this:

Remove the lugs from a junk 1911 barrel. Load up a squib round with
a 230-grain jacketed bullet and about one grain of bullseye. Betcha the slide cycles with the bullet stuck about throat deep in the barrel.

And awaaaay we go!

 

[JohnKSa]

The locking lugs aren't locked when the gun goes to battery either, neither...If they were, you couldn't pull the slide back...

Sure you can--but the barrel comes with it for the first little bit since they're locked together.

Why do you suppose that the breechface/boltface is also referred to as the "Thrust Face"? Because there is thrust acting against it. Try grinding the lugs off the bolt on a bolt-action rifle. The rifle won't kick much, but it'll bury the bolt in your cheekbone, I betcha.

Sure, that's why the bolt locks to the rifle so that the entire unit recoils. Just like the slide locks to the barrel so the entire slide/barrel unit recoils.

but it's still not locked until it goes bang.

I'm assuming you're talking about the tiny amount of play that exists between the barrel/slide in some cases and designs, but that's not true in all of them. Some firmly lock the barrel to the slide when in battery. Function is the same whether or not there is a tiny bit of play between the slide & barrel due to locking "slop".

Hypothetically pull the bullet through the barrel at the same rate of acceleration...slide no move. Block the barrel so that the bullet can't move and slide no move because an equilibrium is struck and remains until pressure drops.

Yes and no. In the first case, the acceleration is being provided by something out side the gun, that outside something will experience recoil, the gun will not. IN the second case, nothing moves so there is no recoil ANYWHERE. The lack of recoil is a result of a lack of motion and without motion there is no momentum and without momentum, there is no recoil.

Block the barrel AND remove the locking lugs, slide move double fast. Why? Pressure drive slide rearward...THEN conservation of momentum is established

Even if you don't block the barrel, the slide still moves double fast without the locking lugs because you have effectively reduced the amount of mass (by not locking the barrel to the slide) in the momentum conservation equation. Less mass but the same momentum to be conserved = more velocity. Conservation of momentum/recoil drives the slide rearward in either case. Ok, now about blocking the barrel--by doing that, you have now made the barrel into the breech and the slide is now a captive projectile driven by pressure.

Why would simply adding locking lugs change the physics?

It doesn't, but the slide velocity will get unmanageable with higher powered firearms unless you make the slide very heavy. Increasing the firearm's power means more momentum to conserve and if you don't add mass to the slide, you get more slide velocity. JMB's design effectively added mass to the slide but without adding it to the handgun--by allowing the barrel to move a little and by locking the barrel to the slide while in battery, he increased the mass of the unit that the recoil was acting against. Because when the recoil was imparted, they were locked together, the recoil acted against their combined mass and therefore the resulting velocity was much lower than if the recoil had been imparted entirely to one or the other.

Look at a blank firing pistol. There is no bullet to cause recoil...yet the slides cycle.

Different story--I touched on that earlier when I briefly mentioned the jet effect. Still recoil, still conservation of momentum, but now the mass is the gases being expelled and the velocity is the velocity of those gases. The jet effect can only happen when gases start to escape so that rules it out as being a factor until the bullet exits the barrel.

Remove the lugs from a junk 1911 barrel. Load up a squib round with
a 230-grain jacketed bullet and about one grain of bullseye. Betcha the slide cycles with the bullet stuck about throat deep in the barrel.

Yes, but that's a straight blowback now. Since the breech is not locked, the gas pressure now acts rearward against the slide/breechface and the barrel/stuck bullet act as the new breech. You effectively turn the slide into a (captive) projectile and make the barrel/bullet the breech.

Ever played with an AR-15/M-16 with a blank-firing device? That's a locked-breech design too...yet when you install a suitable device it functions without a bullet.

That is REALLY mixing things up. The gas pressure from the powder combustion inside the barrel unlocks the bolt via the gas tube indepently of recoil. The BFD is designed to restrict the gas exit at the muzzle to ensure that there is enough gas pressure getting through the tube to cycle the bolt via the gas tube. A COMPLETELY different mechanism entirely and with no relevance whatsoever to this discussion.

 

[ClarkEMyers]

Some of the silenced pistols Hushpuppy style operated locked

Some of the silenced pistols Hushpuppy style operated locked - IIRC there was little or no velocity change locked or unlocked but I could well be wrong.

I don't hear about lower bullet velocities with limp wristing and higher velocities with firm holds but I do know the Ransom Rest can be just a tad harder on a 1911 - might be a good idea to use a buffer - so I suppose there must be some slide velocity effect someplace.

 

[JohnKSa]

but I do know the Ransom Rest can be just a tad harder on a 1911

Not because the slide is going faster, but because it's brought to a stop more abruptly. Your hand is a better cushion than the Ransom Rest.

 

[1911Tuner]

Pressure Does the Trick

Good points John, and I'm somewhat in agreement...but the burning gasses sets the whole thing in motion...bullet and slide...by forcing them in opposite directions. In order for there to be a conservation of momentum, there must first be movement. (of the slide) No movement...No momentum.

Ever seen locking lugs shear off? How about battered and deformed? What does that? Pressure. Pressure that drives the two components in opposite directions at some 20,000psi. Which face on the barrel lugs takes the brunt? Front or rear? How about the matching abutments in the slide? Ever wondered why and how early barrel lugs were equalized with proof loads?

No John...The bullet's acceleration alone doesn't cause the slide to recoil.
Can't happen. The slide recoils because the gasses drive the case back against it while they drive the bullet forward. The slide pushes the bullet and the bullet pushes the slide by way of that pressure wave. They both move at the same instant, but the heavier slide accelerates more slowly...and that greater mass/weight draws everything rearward. maybe I should have said that the conserved momentum just carries longer because of the greater weight.

Think about it...Why do overpressured rounds swage the breechface irregularities or the extractor recess into the case head? Pressure...Why do pistols with excessive headspace blow the case heads? Because the case moved out of the chamber as the pressure drove it backward toward the slide which wasn't quite locked to the barrel yet...and the slide moved away from the barrel, creating a gap that let the case back out... and the area forward of the web lost chamber support.

Chamber pressure operates the locked-breech, recoil operated pistol and the straight blowback pistol by exactly the same mechanics. The blowback is "locked" by the spring and slide mass, while the recoil operated gun locks by the mechanical coupling of the locking lugs...under pressure. The blowback design must also allow chamber pressure to fall before the slide separates from the or the case will blow. Use a lightened spring in one, and it will create an "excessive headspace" condition when the slide moves too quickly..just like the locked-breech/recoil operated design does when an excessive headspace condition exists.

Standin' by...

 

[JohnKSa]

but the burning gasses sets the whole thing in motion

Yes, by moving the bullet. Nothing moves until the bullet moves.

Now, I have been assuming from the beginning that we're not talking about catastrophic failures. Obviously if you shear the locking lugs then the system is no longer operating as JMB intended and all bets are off. I haven't really thought through the way things work when the gun actually blows up, and I'm not going to because it's a different mode of "operation". Well, not really of operation--a different mode of non-operation. Ok, I don't know what it is, but it's not the way things work when things are working. Ok, that's all I'm going to say about stuff breaking--

The slide recoils because the gasses drive the case back against it while they drive the bullet forward.

The slide RECOILS because of conservation of momentum. That's what recoil is, conservation of momentum. And momentum is mass times velocity. Velocity implies motion and therefore nothing recoils without motion. Until the bullet moves there is no motion and therefore no velocity, and therefore no momentum and therefore no conservation of momentum and therefore no recoil.

ONCE the slide is unlocked from the barrel (which can only happen when recoil causes the barrel/slide unit to move far enough to unlock) THEN the slide may move backward under both recoil and also under the force of any remaining gas pressure in the barrel. My guess is that the bullet is pretty much gone by the time the barrel unlocks from the slide so that the remaining gas pressure is pretty much nil. So that gets us back to the slide moving only from recoil.

If you want to see if the slide moves from pressure or recoil, get a long thin punch and a pistol with a threaded barrel. Thread the barrel into something that you can clamp into your vice. Now put the punch down the muzzle against the breechface. Now whack it for all you're worth with a big sledge. You may shear the locking lugs or punch out the breechface, but you'll find out that pressure against the breechface won't unlock the slide from the barrel. This experiment might also convince you that the barrel and slide ARE actually locked together.

But you say, what about if you don't put the barrel in a vise? That's different--THEN, you're acting against the slide and barrel as a UNIT and they WILL move back together until the breech unlocks. But, pressure is INSIDE the chamber and can't affect the slide and barrel UNIT, only the breechface and the bullet. THAT'S the point. RECOIL affects the slide/barrel UNIT while pressure only pushes against the breechface from the inside without moving the barrel.

Think of someone standing in the chamber trying to push the gun open by pushing on the breech. He won't be able to because he's standing on the barrel which is locked to the breech. (Like trying to push your car while you're inside it.)

Now, if he can move the entire slide/barrel unit somehow then the breech will open on its own--but he could only do that from the outside--NOT the inside. Pressure (the guy in the chamber) can't move the entire unit. He CAN push the bullet because it's not fixed to the barrel or breech. By moving the bullet he can induce recoil. Recoil affects the entire unit and THAT'S what unlocks the breech.

Why do overpressured rounds swage the breechface irregularities or the extractor recess into the case head? Pressure...Why do pistols with excessive headspace blow the case heads? Because the case moved out of the chamber as the pressure drove it backward toward the slide which wasn't quite locked to the barrel yet...and the slide moved away from the barrel, creating a gap that let the case back out... and the area forward of the web lost chamber support.

Darn, you want me to talk about things breaking again. The forces exerted against the breechface and case head are MUCH, MUCH higher in this situation, and what you're seeing is the effect that OVERpressure has on metal. It can force the slide back by deforming the locking lugs enough to let the case head blow out, and also the OVERpressure against the breechface is sufficient to cause all kinds of deformation. Again, this type of thing is WELL outside the scope of the way the pistol was intended to operate and you can only draw limited conclusions from it.

Chamber pressure operates the locked-breech

Well, in a sense, chamber pressure operates any firearm, but that's only indirectly true in this case.

The blowback is "locked" by the spring and slide mass

It's not locked at all. That's why you have to keep the power low or make the slide very heavy. The velocity of the slide in a blowback is due to recoil (conservation of momentum) and if it moves fast enough, it will open before the pressure has fallen to safe levels. The proof is that blowback operation is not PRESSURE limited, it's MOMENTUM limited. You can make a safe blowback gun with a high pressure cartridge if you properly deal with the momentum by making a heavy slide. On the other hand, even a low pressure cartridge will cause problems if you don't properly deal with the momentum. And yes, the spring force does play into it. The velocity of the slide will be affected by the spring as well as the mass.

 

[1911Tuner]

re: Recoil

Yeehaa! We're gettin' close, John...but we ain't quite there yet.

First...Chamber pressure drives the slide and the bullet in opposite directions.
No other way it can work. That force gets things moving, and that's how momentum is established.

Going back to Keenan's demonstration with the bolt through the barrel blocking any bullet movement proved that if the bullet doesn't move, the slide won't move...which I have no argument with. The bullet HAS to move...but it's not bullet movement that causes the slide to recoil.
(Rather, it ALLOWS the slide to recoil because its movement breaks the equilibrium.) His bolt caused a forced equilibrium between bullet and slide. The bullet resisted acceleration by exactly the same amount of force that was applied to it, and as long as the force is applied...nothing moves. It's like trying to do a push-up with someone pushing down on your shoulders with the same amount of force that you exert in trying to push yourself up. Equilibrium!

Remove the locking lugs from this machine, and I assure you that the slide will move.

Extend the bolt from the end of the muzzle and pass it through a heavy steel plate..and thread a nut on it. Weld the butt of the gun to another heavy steel plate so that the frame is fixed. NOW...the breech is locked. Pull on the slide 'til the cows come home and it won't move until you exert enough force to move the plate that the barrel is bolted to and thus overcome the equilibrium. Again...Remove the locking lugs and the slide will move.

Stand a barrel on the ground and fire the round. The ground becomes the breechblock. The case will stay and the barrel and bullet will launch. Fire the round horizontally without a "breechblock"...and the case becomes the bullet. The bullet and barrel are the more massive/resistant objects...the "breechblock...for the force to push against.

Remove the locking lugs from the bolt on a bolt-action rifle and fire it. The bolt is now the bullet and the bullet becomes the breechblock...and the rifle itself will recoil forward because the force that is between the bolt and the bullet will push them in opposite directions. Restore the locking lugs and the bullet will accelerate...and the rifle will kick backward because the force is transmitted through the thrust face of the bolt to the locking lugs, which in turn transmit it to the receiver which is attached to the stock.

The notion that (only) the bullet's passage through the barrel somehow causes the gun to kick and the slide to cycle isn't the reality of the event.
There MUST be a unit of force between the two. That force, applied to the base of the bullet and the face of the slide through the case is what drives both, and establishes the momentum...in the first .100 inch of travel. At .100 inch, the barrel starts to unlock. The bullet must be gone and the chamber pressure MUST be at or near zero to prevent a case head blowout.

Cheers!

 

[JohnKSa]

it's not bullet movement that causes the slide to recoil. (Rather, it ALLOWS the slide to recoil

You need to stop using the word recoil if you're going to attribute the motion to something other than conservation of momentum. Recoil is due to conservation of momentum, not pressure--there's really no room for debate on that issue. Basically until something moves there is no recoil.

ONCE the slide unlocks then the pressure can act both ways, so to speak, but not until then. But by the time the the slide unlocks, the bullet is gone and so is the pressure. (As you note.)

Remove the locking lugs from this machine, and I assure you that the slide will move.

That's a different mechanism though. It makes a lot of sense that you want to get rid of those pesky locking lugs because they're exactly what proves that what is moving the slide/barrel unit is NOT pressure.

The pressure can't move the slide for the same reason that you can't push your car while you're inside it. The ONLY things the pressure can push against are the barrel and slide and bullet. The barrel and slide are locked together so there's no way to get any purchase on one to move the other. The ONLY thing that is movable in the beginning is the bullet because the pressure can displace it since it's not locked to the slide or barrel. When the bullet starts moving, recoil starts the barrel/slide unit moving as well and that's what operates the mechanism.

If you can explain how to push your car while you're inside it then you can explain how the pressure moves the slide/barrel unit from the inside.

 

[BluesBear]

Barnyard Physics wun oh wun

I actually understand what happens, so let me see if I can translate it into comprehensible polysyballic units.

The burning powder creates gas pressure that attempts to expand in a 360º SPHERE.

The cartridge case expands against the chamber walls and therefore can expand no further.

Therefore the gasses push against the base of the bullet and the base of the case.

The bullet being the path of least resistence begins to move first.

However the pressure is rising faster than the bullet can move therefore the pressure against the base of the case forces the case to press against the breech AKA the slide.

The slide attempts to move but is locked together with the barrel.

As the bullet leaves the muzzle the pressure rapidly drops to atmospheric levels.

However the pressure againstthe breech face has created momentum.

The rearward pressure/momentum overcomes the sideways pressure/friction and the case begins to slip in the chamber.

As the slide and barrel unit moves rearward the barrel is pulled away from the slide.
This leaves the slide along to continue with the remaining momentum and continue on its merry way until forced to stop by the dustcover reaching the base of the guide rod.

During this movement the recoil spring has been compressed and when the slide stops moving uses it's stored energy to force the slide back forward where the barrel is once again forced back into lockup with the slide thereby restoring the total mass of the slide/barrel unit.

 

[1911Tuner]

re:

BluesBear...Bingo!

John...In the last response...I know that the straight blowback doesn't lock.
That's why I wrote "LOCK". I suppose that I should say "movement" instead of "recoil" but I digress.

Keep in mind that the boltface/breechface/breechblock is technically a thrustface. The recoil-operated firearm works by exactly the same forces as the straight blowback...which is why I keep going back to hypothetically removing the lugs...in order to demonstrate that reality. I guess that the recoil-operated pistol could be more accurately described as a variable slide mass blowback...because the force generated by the expanding gasses get everything in motion. Once the bullet moves, the equilibrium is broken, and the slide will move. If the bullet CAN'T move due to a solid blockage, the equilibrium remains...and nothing moves.

The car analogy is flawed. If the car were cut in half..and I were strong enough to overcome the weight of the two halves, I could move them while sitting inside. If the barrel and slide were welded together at the hood and breechface and the gun fired, nothing would move either...but because the
barrel and slide are separate...and the slide pulls the barrel rearward to the unlocking point...it moves. Back to the car...If I were sitting in the seat, straining to separate the two halves which were tied together by a cable...and the cable were suddenly removed...they'd move in opposite directions, assuming that I were able to exert enough force to overcome the mass.

A physics professor described it many years ago to me like this: (Simplified)
"The rifle pushes the bullet and the bullet pushes the rifle. The heavier the bullet...mass...the more resistance it offers to acceleration and the harder it pushes. The heavier the rifle, the more it resists being pushed. Remove the rifling in the barrel and the rifle will kick less. Go to a higher rate of twist, and the rifle will kick harder because of the increased resistance on the bullet...AND...the rifle's recoil will last longer due to increased bullet dwell time in the barrel. That's why a light fast bullet causes a quick slap, while a heavy slow bullet causes it to feel more like a push. The light, fast bullet stings more, while the slow, heavy bullet moves the shooter farther.

In the theory of the bullet movement (alone) causing the slide's rearward movement, the bullet would first have to act on the barrel, since that's what it's attached to via friction...and the barrel would move rearward first, driving the slide.

This would make it necessary for the REAR faces of the barrel lugs to impose on the FRONT faces of the slide lugs...and that just ain't what occurs. Instead, the front faces of the barrel lugs impose on the rear faces of the slide's lugs under pressure while the force between them attempt to drive them in opposite directions. This is why we see flanging and deformation of the lugs in a high mileage pistol. If there is a sloppy barrel to slide fit, giving the two components a running start at each other, we see evidence of "slap seating" with the telltale stair-step shape on the lug tops in both barrel and slide. It occurs at the front faces of the barrel lugs, and the rear faces of the slide's lugs. In the other theory, this would be reversed.

A bolt-action rifle does reverse it. The barrel is fixed and the force acts rearward on the thrustface..driving the bolt lugs BACK into the recesses in the receiver...and deformation occurs at the rear faces of the lugs. File
.015 inch off the rear faces of the bolt's lugs, and the bolt will move rearward by a like amount upon firing. Headspace increases, and a case head separation will likely result.

Do a vertical push-up with your hands against a friend's shoulders. if you both weight the same, you'll both move an equal distance. If one is 50 pounds heavier, you'll both move, but the heavier one will accelerate more slowly...but you'll both move. Equal and opposite directions as a result of a unit of force BETWEEN you. The force is provided by your arms...just like the force in the chamber provides the push for both slide and bullet. The bullet accelerates faster, but the slide conserves its momentum more efficiently...and it pulls the barrel rearward to the unlocking point.

Read this carefully because this is the reality of the event....When the barrel reaches the unlocking point, the breech starts to unlock...If the bullet is still in the barrel at that point, chamber pressure is still high...probably at or near peak. The case will back out of the chamber under that pressure, and a blowout will occur. The bullet MUST be gone so that the pressure can drop. The barrel unlocking sequence begins at 1/10th inch of slide travel....and the momentum necessary for the cycle is established. If the breech unlocks BEFORE pressure drops, ka-boom.

 

[horge]

I was about to dig into a burrito while browsing this thread....
but all the talk about burning gases inducing all kinds of movement gave me pause.

Nice discussion, guys.
Cheers.

 

[CAnnoneer]

Does anyone know what percentage of a rounds energy is used to operate an auto. I am sure it varies among guns, but is it a consideration. It would sem that the less energy required to operate the mechanism, the more energy would be added to the rounds velocity.

This is a simple physics question.

Gunpowder ignites and burns creating gas at very high pressure. The gas pushes against the bullet and against the back of the cartridge, and thus the pistol.

At this point the pistol as a whole can be considered a closed system. Momentum is conserved in a closed system due to Newton's 2nd Law (Foutside=dp/dt so Foutside=0 means p=constant). Thus the gun and the bullet moving in opposite directions gain momenta of equal magnitude.

p=mV=Mu

where:
m=mass of bullet
V=velocity of bullet
M=mass of pistol
u=velocity of pistol
p=momentum of pistol=momentum of bullet

Now the energy of the blast is distribute among generated heat, kinetic energy of the bullet, and kinetic energy of the pistol. For simplicity, let's ignore the heating. Then the energy E is

E=(mVV+Muu)/2

Combining with above, we get

E=pp/(2m)+pp/(2M)=(pp/2)(1/m+1/M)

Then the fraction of the total energy that goes into the pistol is

f=Epistol/E=(1/M)/(1/m+1/M)=1/(M/m+1)

Now different things need to be plugged in for different systems.

A revolver weighing 1 kg shooting a 10g bullet would gain about 1% of the available energy as kinetic energy if shot in free space without propping (M=1kg). If you grab it hard, then YOU become the gun, so M=your mass. So the fraction will be far less than 1%.

A blowback has a heavy slide that can be approximated as a free-space pistol, so M=mass of the slide. If M=300g, then 3% of the available energy becomes "wasted" on action.

A locked-breach would function someplace in the middle between revolver and blowback, because it behaves like a revolver until the breach opens, and then it functions as blowback.

Anyway, I hope this makes things clear.

Incidentally, the same line of thought explains how limp-wristing would produce failure to eject and/or feed. If you do not limp-wrist, the pistol does not move, so the slide gets enough of the recoil energy to stretch the main spring enough far back because

W=kxx/2

Where
W=work needed to be done on the spring to stretch it by distance x
k=spring constant
x=stretching distance (elongation)

If you limp-wrist, the pistol is allowed to travel, so part of the energy goes into accelerating the pistol itself. The slide gains less kinetic energy and so does less work W against the spring before it stops. Elongation is decreased, so the slide does not get sufficiently far back.

Any questions?

 

[BluesBear]

horge, regarding the forces and momentum of burrito gas;

#1 There is more room outside than inside.

#2 Better out the front door than the back.


Bone apateet y'all!

 

[JohnKSa]

"The rifle pushes the bullet and the bullet pushes the rifle. The heavier the bullet...mass...the more resistance it offers to acceleration and the harder it pushes.

Perfect description of recoil. Doesn't exactly say that pressure is what causes recoil though.

The car analogy is flawed. If the car were cut in half..and I were strong enough to overcome the weight of the two halves, I could move them while sitting inside.

But the gun isn't cut into two halves. It's a slide/barrel unit that is locked together plus a bullet. And the car isn't cut into two halves either. There IS a way to push the car from the inside that works without cutting the car into pieces. You can push it from the inside by throwing something out the back at high velocity and then recoil will move the car. That is EXACTLY what happens in the case of the firearm. The pressure pushes the bullet out the front and the recoil moves the slide/barrel unit back.

There's no question that the PRESSURE is the mechanism that causes movement, but the PRESSURE can't do squat as long as the bullet remains in place. It's trying to push the car from the inside. When the bullet is thrown out of the barrel by the pressure, recoil is generated and THAT moves the "car".

The bullet being the path of least resistence begins to move first.

Barring a catastrophic failure, the bullet is not the path of LEAST resistance, it is the ONLY thing that the pressure can move, period. The locked breech ensures that.

I think we're all sort of saying the same thing, but mixing the terminology badly.