Energy Used To Operate An Auto

[BluesBear]

In a self contained metallic cartridge the bullet is a safety valve.

But the gun isn't cut into two halves

No but the cartridge is. The bullet is one half and the case is the other. And the cartridge is where the pressure originates.

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.

My analogy encompasses both locked, retarded blowback and pure blowback action types.
The bullet, being of lighter weight/less mass is easier to move than the cartridge case which is in contact with the chamber/breechface and therefore its movement is governed by the total mass. So the bullet offers the least resistance. Just like a safety valve.

Put a strain gauge on the chamber, prevent the bullet from moving and fire the cartridge. The pressure will be a LOT higher than normal. This is how Kabooms happen.

 

[JohnKSa]

No but the cartridge is.

The cartridge is moot to this discussion since the operation in a locked breech pistol will be the same with or without it.

Put a strain gauge on the chamber, prevent the bullet from moving and fire the cartridge. The pressure will be a LOT higher than normal.

Exactly, and yet even with all that extra pressure the slide/barrel will not move. So pressure can't move it--at least not without moving the bullet first...

 

[BluesBear]

For those out there who apparently can't take a subtle hint...

The original question in this thread is;

Does anyone know what percentage of a rounds energy is used to operate an auto.

NOWHERE does the question specify locked breech or 1911 type action.
:banghead:

NEWSFLASH !!! ​

Not all automatic pistols use a locked breech.

That's why I have been speaking about automatic pistol actions in general.
That is why Tuner was also stating what would happen if the locking lugs were removed from the equation. And why he mentioned what would happen in a sealed breech firearm.

You cannot state what happens with a locked breech autoloading firearm as an absolute regarding all other types of firearms.

When the primer ignites the powder in a self contained metallic cartridge the gsses created really don't give two hoots in hades what type of firearm is attempting to contain it.

It just expands.

After all, that's its job.

 

[BluesBear]

Oh yeah one more thing. The cartridge is NOT moot. The cartridge and the adhesion of the case sides to the chamber walls is extremely germain to the operation of several types of autoloading actions. The fluted walls of an HK chamber, for instance, are there to increase adhesion thereby delaying unlocking.

Without the cartridge case the pressures are acting directly against the chamber walls. And therefore if the bullet was prohibited from moving at all there would be no direct physical connection between it and the breechface.

If it were a straight blowback action the slide would most assuredly move to the rear with extreme force.



In another example, take a persussion cap fired muzzle loading rifle.
Load it normally.
(I'm sure many of you recall this example as being from the Civil War.)
And then in the heat of battle, load a couple more loads on top of it.
When the first load decided to fire, (it was suspected that damp percission caps were malfunctioning) the extra resistance of the multiple loads prevented the first bullet from moving.
The excess pressures attempted to vent out the flash hole. (AKA the path of least resistance)
It succeeded and in doing so fractured the nipple and forced the hammer back past full cock with enough force to break the mainspring.

 

[Erinyes]

BluesBear gave the best description of how the system works. Pressure from the burning gasses expands in every direction. Everything that can be moved will be moved at a rate of acceleration based on it's mass. So at the same instant that the gasses begin pushing the bullet down the barrel, they're also pushing the cartridge case both against the chamber walls and the breachface. In turn, the entire case/barrel/slide assembly moves backwards because of the gas pressure.

Ever thought about why the locked-breech, short recoil design is necessary? It's because in larger pistol calibers (say around 9x19mm), the gas pressure is able to accelerate the slide reward too quickly. The breech is opening before the bullet has exited the barrel, and the pressure in the barrel is too high. Therefore, you have a case blowout.

Of course, no one has actually answered the question in the OP. What percentage of an auto pistol's reward momentum is absorbed by the slide's action. Though I'm sure it's very different between blowback and locked-breech actions. However, it seems that with it's greater moving mass, the locked breech design would absorb more energy, not less, than a blowback pistol.

 

[CAnnoneer]

Of course, no one has actually answered the question in the OP. What percentage of an auto pistol's reward momentum is absorbed by the slide's action.

The question was about energy, not momentum, and I did answer it in my post - less than 3% for a locked-breach pistol.

 

[1911Tuner]

re:

John Said:

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

I think you're right, John... but we've almost come to a rendezvous point.

Erineyes and Bluesbear...thanks for simplifying it.

I agree that unless the bullet moves, the slide will not cycle. No argument at all on that point. It HAS to move...but the bullet's movement doesn't generate some mystical, magical force that moves the slide. The bullet's movement upsets the equilibrium established in that first nanosecond of ignition when the pressure was trying to get it swaged down and into the rifling and trying to drive the slide rearward at the same time. When the bullet moves, the equilibrium is upset...and the slide moves. Once it moves, momemtum is established. Remember...For a very brief instant, nothing will happen because of inertia and friction. (Objects at rest tend to remain at rest until overcome by...)

Back to the car thing...Okay, I blew it again...but suppose that I, through a
herculean effort, were able to literally rip the front half of the car from the rear after straining for 3 seconds. Then things would move. Fling a heavy object out the back of the car, and the car would "recoil" forward. Right-O...
but when we do that, there is a unit of force pushing in opposite directions
on both the car and the flung object. Same thing. The fact that the object was flung doesn't move the car...Rather, the FORCE that flung the object
pushing in opposite directions on car and flung object moved both.

Pick up a heavy medicine ball, hold it against your chest and PUSH. The ball moves...You move...The force that caused it was in your arms. If some magical, mystical force snatched the ball out of your hands...you wouldn't move unless you tried to hold on..and then you'd follow the ball. If youand the ball are tied together by a rope, when the ball moved far enough to take the slack out of the rope, your mass would stop the ball and reverse its direction...just like the slide does with the barrel.

And I did so answer the question, Bear! I just didn't know the equation(s) to provide a percentage.

So...Kuhnhausen's "Balanced Thrust Vector" does exist. It just doesn't happen WHERE he states...after the bullet exits. It happens at ignition,
and breaks when the bullet moves. Jerry knows his stuff...He just doesn't put it into words very clearly. (Kinda like me, sometimes)

 

[Jammer Six]

Here's how I think it works:

Oh, wait...

I don't know a damned thing about it...

Popcorn. I'll fix the popcorn.

 

[1911Tuner]

Popcorn

Jammer...About as simple as I can make it.

When you go buy another gun, and SWMBO finds out and punches you at mid-torso...You both stagger backward. You're the bullet...She's the slide...
the punch is the force between you that pushes you both in opposite directions. Of course...assuming that you're actually the heavier of the two, reverse everything.

 

[BluesBear]

And I did so answer the question, Bear!

It wasn't me who said you didn't.
I think I said that you had. (and in several ways)



Anyway we have left out one important factor...









(hang on to your popcorn Jammer)











Headspace!

 

[JohnKSa]

but the bullet's movement doesn't generate some mystical, magical force that moves the slide

I'm not saying it does. But the motion of the slide is a function of conservation of momentum. No argument that the pressure is what MAKES the momentum happen and I guess you could work it back and eventually get pressure to plug into the equation but that's taking the long way around. Besides, then you get into a situation where you have to take bore diameter and a lot of other variables into account. Momentum and conservation of momentum are well defined and easily quantifiable parameters that account for slide motion. Mathematically relating chamber pressure to slide motion would be far more complicated and the entire derivation would have to be started from scratch and repeated for each different caliber and load you wanted to analyze.

The cartridge is NOT moot. The cartridge and the adhesion of the case sides to the chamber walls is extremely germain to the operation of several types of autoloading actions. The fluted walls of an HK chamber, for instance, are there to increase adhesion thereby delaying unlocking.

The cartridge plays a part, but it doesn't change the overall operation of the JMP locking breech pistol design. It certainly affects a lot of things, but the overall way the system works can be understood and discussed without bringing the effects due to the cartridge case into the discussion. It plays a more critical role in other designs and can't be ignored in those designs.

 

[grendelbane]

Does anyone know what percentage of a rounds energy is used to operate an auto.

Taking a Gov't model .45 ACP as an example, I calculate that less than .075% of a rounds energy is used to operate the action. But, since I am not a professional mathematician, and don't play one on TV, it will be extremely difficult for me to explain how I came to my conclusions.

For those who want to try anyway, here are the figures I used;

230 grain bullet travelling at 840 FPS.

Slide velocity is 23 FPS.

I have conveniently ignored the powder charge, both its weight and its muzzle velocity.

Other pistols will come up with a different figure, but it probably will not stray too far.

Revolvers lose more through the barrel/cylinder gap.

 

[grendelbane]

My other answer is less than 2.78%

Remember, only one of these answers can be correct.:banghead:

 

[1911Tuner]

Slide Speed

Grendlebane...Somewhere I remember reading that the slide's average speed
for the complete cycle was just over three fps...timed during a stop-action video with total distance traveled...comin' and goin'... plugged in.

Wish I could remember where I saw that. If I can find it again, I'll post a link to it. Interestin' stuff.

John my man! It looks like we've either reached an agreement, or an impasse...I'd rather think it's an agreement. You're a tough customer.

 

[JohnKSa]

It looks like we've either reached an agreement, or an impasse...I'd rather think it's an agreement. You're a tough customer.

Yes, yes and same to ya.