Hydraulic recoil spring?

[barnbwt]

"It's so hard to not be snarky"
Then take a break (for a couple hours)

Guys, do please try to avoid getting the thread locked before I have a chance to put up some free-body diagrams in an hour or so...I'll be seriously bummed if this interesting (if needlessly heated) conversation gets shut down.

The real problem I'm seeing is that a math problem --which is what friction/momentum/etc. are-- is incredibly hard to articulate in words (see "trains leaving Baltimore at 3mph and 50mph..."). Which is why I think free-body diagrams will be helpful in at least clarifying the various viewpoints (which I now think are all 'proving' exactly the same things, but we're arguing over which of two separate conclusions --both accurate-- are correct)

My FBE's;
-Slide locked w/ barrel, during period bullet in in the bore; solving for an equation that determines slide/barrel group initial speed (assuming bullet reaches muzzle velocity instantly, which is good enough for bulk slide momentum calcs)
-Barrel camming down (not a 1911 expert, so this will probably have a bad assumption somewhere, but it kinda matters not if the action is depressurized at this point). The goal is to find momentum of barrel/slide as they decouple
-Cartridge extraction once barrel is arrested (examining how extraction forces may affect slide dynamics)

TCB

 

[JRH6856]

Ok on a Glock, (also browning tilt) the slide locks to the barrel via the barrel hood. So that's the locking lug equivalent.

I am not talking about Glocks. I don't know enough about Glocks to presume to discuss their action to this degree of detail. I thought we were talking about the 1911. Since we apparently are not, then I have no reason to continue and I apologize for interfering with whatever you are doing.

 

[GLOOB]

No snark.

Tuner, I don't own a luger, so I cannot explore that thought exercise. But I will attempt to explain any and all ideas that anyone presents. Without dancing around the subject. I have already addressed most of your ideas, but if I miss anything you feel is significant, please bring it to my attention.

Here's one of your latest posts which I will address:

Think hard, and consider one more piece of evidence on this video.

If that had been a straight blowback with the same slide mass and spring...it would have wrecked his thumb and wrist.

But it didn't. He was able to keep the slide from budging without even straining.

http://www.youtube.com/watch?v=Gw8sbb8eDjg

I assume you are referring to someone keeping the slide closed with their thumb, shooting a locked breech pistol.

In a locked breech pistol, the slide is locked to the barrel. When the bullet is pushed through the rifling, that 100 lbs of force of swaging and dragging the bullet through the barrel is not translated into movement of the slide backwards. This is because the slide is locked as one with the barrel. The only thing that "feels" this force is in regards to increased force between the lugs on the slide and barrel. So what IS pushing back on the slide is simply the unadultered conservation of momentum. The only thing your thumb need overcome is the 230gr x 900 fps of momentum, which is not that much. In fact, when you press your thumb over the slide, you are simply spreading out that momentum. Instead of just the slide moving back, the entire slide, frame, and your hand and arm are gaining that ~200,000 grain-feet/s of momentum.

Whereas in a High Point, the slide must also necessarily react to the force needed to swage that bullet into the rifling. And the force needed to overcome friction, (which turns into heat). So if you did this with a High Point, you would fail?

In other words, you must consider the contribution of bullet swaging and heat energy when you consider the slide momentum in a High Point, but you can rightly ignore it when you consider the slide momentum of a locked breech pistol?

Yes, no, maybe? What are your thoughts on this? Why did you ask me to think hard about this example? What do YOU think about it? What do YOU take away from it that convinces you that you are correct? Please don't give me a different analogy and ask me to think hard about it. Let's finish this one, first? You see something I don't. Walk me through it.

 

[GLOOB]

I am not talking about Glocks. I don't know enough about Glocks to presume to discuss their action to this degree of detail. I thought we were talking about the 1911. Since we apparently are not, then I have no reason to continue and I apologize for interfering with whatever you are doing.

Change "locking block" to "cam-over point" and you know everything you need to know about a Glock. No need to apologize. I am not offended, insulted, or slighted. I am just perplexed.

I apologize. A lot of people consider me a bit of a troll. It happens. I'm ok with that. But in this thread, I wonder if I'm not being group-trolled in a concerted effort to piss me off.

 

[JRH6856]

Change "locking block" to "cam-over point" and you know everything you need to know about a Glock. No need to apologize. I am not offended, insulted, or slighted. I am just perplexed.

No, it tells me nothing. A 1911 locks up on the barrel/slide lugs. I can't relate this to a "cam-over point" so I don't know what you are calling a "locking block".

The Browing High Power has a cam block that cams the barrel down after it unlocks, but it is not a locking block. The BHP locks up the same way as the 1911—the barrel/slide lugs.

 

[1911Tuner]

In a locked breech pistol, the slide is locked to the barrel. When the bullet is pushed through the rifling, that 100 lbs of force of swaging and dragging the bullet through the barrel is not translated into movement of the slide backwards.

Nobody said that it translated into the slide's movement backward. I said that it resisted the slide's acceleration, and three mechanical engineers have agreed with me...two of them with over 50 years collective experience.

So what IS pushing back on the slide is simply the unadultered conservation of momentum.

Nope. What is pushing on the slide is 20,000 pounds psi and expanding gas at peak pressure. Momentum is involved because the gun is moving...but the momentum is a mousefart compared to the acceleration. Once the bullet exits, you're feeling conserved momentum...but the guy kept that slide from budging with one thumb. The slide itself never moved...so it never gained any momentum of its own.

Again...if it had been a straight blowback, he'd need an orthopedic surgeon.

The only thing your thumb need overcome is the 230gr x 900 fps of momentum, which is not that much.

If you really believe that, fire a 1911 without the spring, and hold the back of the slide a half-inch from your nose.

And for the record...some parts of your argument do sound like you're describing a straight blowback. For instance, the heavy bullet/early unlocking theory will work with a blowback because the barrel isn't tied to the slide, and the bullet's forward drag on the barrel can't affect the slide.

In case you missed it, look at these lugs and the way they're deformed. You can't do that to steel without some pretty serious opposing forces.

This bullet drag and opposing force is the mechanism that stretches revolver frames and leads to endshake...and it's the mechanism that cracks 1911 slides adjacent to the breechface.

Study this picture, and in your mind's eye...see the slide pulling the barrel back against the bullet's opposing drag...and trying to shear the lugs off the barrel. You can even see the original lug face position and how much the steel was displaced.

 

[mls]

Again, outstanding!

 

[barnbwt]

No, it tells me nothing. A 1911 locks up on the barrel/slide lugs. I can't relate this to a "cam-over point" so I don't know what you are calling a "locking block".

A 1911 does not operate significantly different in its cycle than a Hi Power or a Glock. They all lock the barrel to the slide during recoil until such point the barrel is lowered by a cam of some sort (pivoting in the case of the 1911, sliding with a teensy bit more friction in the case of the latter two). Due to the very brief pressure spikes of all pistol rounds, timing must be similar or else they would all rupture or fail to cycle (since the rounds are all so similar, is what I'm trying to say)

TCB

 

[JRH6856]

OK, I just found an animation of a Glock firing sequence

IF this is accurate, the slide is delayed and the barrel does not unlock until the bullet has left the barrel.

It looks like the Glock is locking up on the square chamber shoulder and the front of the ejection port. This would be the equivalent of the 1911/BHP barrel and slide lugs. The camming block below does the same thing as the camming block of a BHP. It cams the barrel down after it unlocks.

But knowing something about graphics and animations, I doubt the timing is accurate.

 

[1911Tuner]

Now then...gentlemen...let's keep this civil.

We're not gonna let this one go down in flames if I have to lock it for 24 hours to give everybody time to take a breath.

 

[1911Tuner]

A 1911 does not operate significantly different in its cycle than a Hi Power or a Glock. They all lock the barrel to the slide during recoil until such point the barrel is lowered by a cam of some sort

The Glock operates exactly like a 1911. It just uses a cam and a cross member through the frame to raise and lower the barrel instead of a link and the slidestop crosspin. The cam/crossmember was first used in the High Power. It's an improvement over the 1911's system because it's stronger...more durable...and less likely to deform, crack, or shear when the lower barrel lug slams to a stop against the crosspin and stops the slide.

And actually, the 1911's lower lug is a cam that raises the barrel...just like the "locking block" that's been described. The link's only function is vertically disengaging the barrel from the slide. That's all it's there for.

And again...the Colt-Browning tilt barrel engages the slide vertically, but it locks horizontally.

Go back and read post 160.

 

[barnbwt]

Okay, got "Installment 1" of the free body diagrams finished. Hopefully this clarifies at least my point of view. I incorporated as best I could tell all the different forces I or others had posited were going on during initial recoil prior to camming.

For those who are unfamiliar with Free Body Diagrams (if we're all engineers, let me know and I'll shut up ), the point is to make a visual representation of the equations used to sum up forces and moments (torques) in a system which describe its static or dynamic operation. In the case of a 1911, the slide essentially moves straight forward and backward (the recoil pitch caused almost entirely by the grip location, I think we can all agree), which means all forces in the vertical direction must balance to zero, as must all moments which would seek to rotate the action (again, looking only at the action; treat the frame as rigid or in a Ransom rest with no deflection)

The main takeaways I found that surprised me is that the frame rails appear to apply quite a bit of load in order to counter act the torque caused by the off-axis forces acting on the slide (the recoil spring and barrel thrust, specifically). Not surprisingly, I found that all the internal frictional forces cancel out when you look at the barrel/slide as a locked unit.

Main assumptions:
-Barrel/slide rigidly locked early in the cycle. If this is disagreeable, please offer a darn good explanation
-Hammer rolled into spring force for diagram simplicity
-Bullet internal ballistics simplified (max speed, max pressure while inside)
-Frame rails frictionless (because they should be )
-Bullet muzzle velocity/momentum inherently accounts for barrel friction

TCB

 

[GLOOB]

Quote:
So what IS pushing back on the slide is simply the unadultered conservation of momentum.
Nope. What is pushing on the slide is 20,000 pounds psi and expanding gas at peak pressure. Momentum is involved because the gun is moving...but the momentum is a mousefart compared to the acceleration. Once the bullet exits, you're feeling conserved momentum...but the guy kept that slide from budging with one thumb. The slide itself never moved...so it never gained any momentum of its own.

Correct me if I'm wrong. You are saying the slide is being pushed by much higher force than the mousefart of the bullet acceleration. I agree, but this is not a concern to your thumb. It's a concern to the locking blocks. So we agree on that?

So what is leftover to actually move the slide, if not more or less the momentum of the bullet? What do you think is moving the slide?

Quote:
The only thing your thumb need overcome is the 230gr x 900 fps of momentum, which is not that much.
If you really believe that, fire a 1911 without the spring, and hold the back of the slide a half-inch from your nose.

Why are you changing the example? Leaving a half inch of space is obviously letting the slide build up kinetic energy before you attempt to stop it. When you keep the slide closed, you effectively add the mass of the frame and your hand to the equation, and the slide starts with zero kinetic energy. In this scenario, the 200,000 grainfeet/s of momentum is "not that much." I just don't understand why you twist and squirm when under the spotlight.

I'm very disappointed with your very superficial analysis of this example. Why should I think hard if you do not?

Again, if not the momentum of the bullet, what do you imagine is the reason for the slide to move back? Forget your locking lugs. What EXACTLY is remaining to move the slide, after the locking lugs have taken all that force and friction and force forward and force backward and other ideas you have in your head?

 

[barnbwt]

"The Glock operates exactly like a 1911. It just uses a cam and a cross member through the frame to raise and lower the barrel instead of a link and the slidestop crosspin."
Believe it or not, I've heard the claim that the arc-shape the 1911 cams down on pivots causes the action to substantially differ in operational characteristics from the linear-ramp cam (with some small amount of friction) found in the Hi Power/Glock (by which I mean SIG ) action

Personally, I call BS on that, but whatever effects there may be are likely beyond our ability to debate effectively (or even measure )

TCB

 

[1911Tuner]

Correct me if I'm wrong. You are saying the slide is being pushed by much higher force than the mousefart of the bullet acceleration.

No. Go back and read it again. Slide and bullet are driven by equal force while the bullet is present...20,000psi. That's what he stopped with one thumb...not momentum. He couldn't have done that with a blowback.

Why are you changing the example? Leaving a half inch of space is obviously letting the slide gain more kinetic energy.

How can the slide gain more kinetic energy after the bullet is gone? There's no force driving it any more. It can't accelerate to a higher velocity. It can only decelerate, and the only thing keeping it in motion is its conserved momentum.

 

[barnbwt]

"Momentum is involved because the gun is moving...but the momentum is a mousefart compared to the acceleration."
I'm not sure what you're trying to say here, since momentum cannot be equated to acceleration (different derivatives and there's no mass in the latter). Could you please rephrase the statement you were trying to make? I might understand it with some different verbage.

Momentum is mass times velocity. Acceleration is the first derivative of velocity, and can be calculated as applied force divided by mass. Rate of change of momentum can be equated to acceleration since mass is assumed constant in our firearm (one hopes )

TCB

 

[GLOOB]

... Tuner, what I'm getting at is this.

You are trying to reduce the momentum of the slide, relative to the momentum of the bullet, in a locked breech system. You loosely attribute this to the locking lugs. "Gee look at the forces on those lugs." Therefore, you are thinking you can ignore conservation of momentum, because some of that must be going towards the beating up on the locking lugs, right? Somehow, someway, are you thinking this?

I am telling you exactly what forces those lugs are taking. And they do not include the acceleration of the bullet. They are taking the force needed to swage the bullet and overcome the friction which you are so crazy about. That is exactly what they lugs are doing.

What you need to think about is ADDING those forces taken by the lugs into the High Point example. Not trying to remove conservation of momentum from the locked breech example.

Please, just think about it.

How can the slide gain more kinetic energy after the bullet is gone?

Between where the slide starts at rest (thumb on the back) and when the bullet leaves the muzzle, (slide aimed half inch off your nose), the slide gains kinetic energy. Not after the bullet is gone. In the first 1/10th inch while the bullet is still in there. Try stopping the slide with your thumb a fraction of an inch off the back. 1/10th inch, or half inch, it doesn't matter. The damage will be done.

 

[1911Tuner]

I'm not sure what you're trying to say here, since momentum cannot be equated to acceleration (different derivatives and there's no mass in the latter). Could you please rephrase the statement you were trying to make? I might understand it with some different verbage.

Be happy to.

When the guy stopped the slide with his thumb, the system was being accelerated under 20,000 pounds psi of force. That's what he stopped with his thumb.

The gun moved, but not the slide. Since the gun was moving, it had momentum. The whole gun. The slide itself didn't gain any momentum of its own because it never moved.

And once the bullet has exited and all force is removed, there is no more acceleration. There is only momentum.

If he had tried to do that trick with a straight blowback with the same slide mass and spring, his thumb would have been ripped from its moorings.

 

[1911Tuner]

You are trying to reduce the momentum of the slide, relative to the momentum of the bullet, in a locked breech system. You loosely attribute this to the locking lugs.

No. The locking lugs only attach the barrel to the slide.

The bullet's forward drag on the barrel affects the slide's acceleration because it resists the barrel's rearward movement...and whatever resists the barrel resists the slide.

I've said this about a half-dozen times since this started.

Read it carefully.

Whatever frictional resistance the barrel offers to the bullet, the bullet offers to the barrel, and whatever resistance is offered to the barrel is offered to the slide.

That's how the guy was able to easily keep the slide from moving, and why he couldn't do the same thing with a blowback that has the same slide mass and spring. The bullet's drag on the barrel can't affect the slide because they're not connected.

I really don't know how else I can put it.

I'm gonna hit the rack now. 0400 comes early at Rotha Manor.

 

[GLOOB]

The bullet's forward drag on the barrel affects the slide's acceleration because it resists the barrel's rearward movement...and whatever resists the barrel resists the slide.

Whatever frictional resistance the barrel offers to the bullet, the bullet offers to the barrel, and whatever resistance is offered to the barrel is offered to the slide.

You keep saying these things, but then turning around and denying it. It's like you say the words but don't get it.

I've said this about a half-dozen times since this started.

Oh, we've all noticed. You repeat it like a mantra.

If you are saying this, meaning this, understanding this, and believing this, then we AGREE.

You REMOVE all bullet frictional force when calculating the slide momentum compared to bullet momentum in a locked breech system... right?

So bullet momentum equals slide momentum, right?

So you are totally agreeing with me but totally saying I'm wrong in the same breath.

 

[barnbwt]

"Slide and bullet are driven by equal force while the bullet is present...20,000psi. That's what he stopped with one thumb...not momentum. He couldn't have done that with a blowback."
Are we sure of that? Because blowbacks almost uniformly have much harsher recoil than locked-breech guns, simply because the shooter is exposed to all of it at the same time (when the slide bottoms out). The recoil you feel at the butt of the gun has to equal that at the muzzle from the bullet (plus the extra from the high speed ejecta), because there is no other force grounded to the Earth acting on the weapon but your body.

What the locked breech does is split the bullet's momentum between the slide and barrel, then arrest one before the other for extraction --this divides the recoil impulse to the shooter. Moreover, because the breech is rigidly locked when pressures are high and breech integrity most critical, the barrel/slide reciprocating weight doesn't need to be anywhere so massive. That's why Bubba'ed 1911's cycle at +1000rpms whereas a Thompson does 500rpm or so; the heavy bolt is needed to keep the chamber from rupturing, while the 1911's only needs to be massive enough to strip rounds reliably.

In a direct blowback, the momentum transfer theory is incomplete since the bullet friction acts on the barrel but not the slide (it acts on the frame directly, instead). The same pressure over the same area drives the bullet and slide equally, but barrel friction slows the acceleration of the former. Work is conserved --force times distance-- but not momentum. Some of the bullet's momentum is diverted to friction/heat instead. I do somewhat question what impact this factor really has at the end of the day for any purpose but designing the barrel retention, since it is only a couple hundred pounds at most compared to the thousands (or tens of thousands) imparted by the pressure to slide/bullet. Now, the component of pressure acting on the cross sectional area of a necked/tapered case can be very significant, but 45acp and even 9mm have pretty low figures, here. The breechface feels the same thing regardless, but the barrel threads (or locking lugs) might not.

TCB

 

[barnbwt]

"I am telling you exactly what forces those lugs are taking. And they do not include the acceleration of the bullet. They are taking the force needed to swage the bullet and overcome the friction which you are so crazy about. That is exactly what they lugs are doing."
Actually, because the slide is being pushed away from the bullet as it is being driven, the mass X acceleration of the bullet is directly related to the same for the slide. The discrepancy by swaging/etc. eats away from the bullet's 'theoretical' acceleration by way of inefficiency. Same reason a shorter piston skirt in an engine is more fuel efficient (though more wear prone)

TCB

 

[barnbwt]

"You REMOVE all bullet frictional force when calculating the slide momentum compared to bullet momentum in a locked breech system... right?"

ONLY when calculating bulk slide+barrel numbers. You MUST include the internal factors when calculating the internal lug interface loads.

Please look at the free body diagrams where I do this exact thing for both

TCB

 

[JRH6856]

What the locked breech does is split the bullet's momentum between the slide and barrel, then arrest one before the other for extraction --this divides the recoil impulse to the shooter.

In a 1911, what is it that locks the breech?

 

[GLOOB]

20,000psi. That's what he stopped with one thumb...not momentum

No. The brass and chamber stop 20,000 psi. Your thumb can't do that. You are simply confusing the issue by switching around ways of looking at it.

Instead of repeating yourself, ask yourself. What makes the slide move? After you remove all the "force forward, force backward" garbage that equal out to zero?