doublegunshop.com - home Forums General Discussion Classic & Custom Single Barreled Sporting Rifles @ doublegunshop.com Pressure or Force

I always thought it was black powder that popped off, i.e., exploded, and smokless that just burned, albeit quickly. I can't try this in a Manhattan apartment but make two equal small piles of the stuff on a steel plate and touch a match to them.

Wouldn't work - especially smokeless will react very differently under pressure when contained. When I burn 58grs of VV N165 in the open, it just burns vigorously. contained in a case with a bullet up front, when fired from a rifle, the result is very different...

Sorry, Michael, I wasn't clear. The use of smokeless is only one of many variables; some smokeless loads would actually be less stressful than some black loads, depending, and I should have emphasized that the burning rates are the main factor. My words weren't intended to be a dogmatic statement of fact under all circumstances, but rather a generalized observation that would, I hoped, stimulate further discussion.

The reasoning behind my words is simple physics. A force applied over a longer time span is less likely to damage an object than the same force applied in a millisecond. The analogy of a fist fight blow comes to mind; the instant application of the strike of the assailant can break bones but if he had just shoved his opponent, even with his full weight, the damage would be much, much less.

Perhaps I should have used a comparison between Bullseye and H4831? Sometimes the term 'black powder' seems to cloud the issue.
Regards, Joe

No expert here, my physics is plenty rusty but here is what I was taught;

F=MA

Acceleration has to be taken into account as does mass in computing force. How to measure the acceleration on the case escapes me. In theory, Newton's third law tells us the rearward force on the rifle is equal to the forward force acting on the projectile. Much of that, however, is acting on the mass of the rifle as a whole. What is the fraction acting on the case head? My instincts tell me it's irrelivent. Measuring pressure empirically factors everyting into account. All that's needed to understand the implications is the area of the case head.

A better question might be, what is pressure? For our purposes it is determined through experimentation with sensors. Most of us can understand crusher testing devices. It doesnt matter how fast or how slow- the copper crusher cylinder will be deformed a certain amount. You can deform it slow with a hydrolic press or fast with a hammer; if it's deformed the same amount, the "pressure" is equal.

I think the bottom line is we are confusing two different vectors. Force might best be visualized as the anvil dropped from ten feet high which hits a bridge- which would normally support it's weight- and crashes through. The acceleration of gravity over distance has acted on the anvil's mass, increasing the force.

Pressure is the amount the anvil deforms whatever it hits; like the copper crusher, it's acceleration is already taken into account.

Is there a engineer/physics professor in the house?

Best,

C.

Last week, I took a 1910 Winchester to the range. It's a blowback in .401 WSL. I have shot it a few times with 4 different loads and maybe it tells us something about force and pressure. The breech block is held shut by a big spring attached to a big weight hidden in the fore end. No locking lugs, but it is a strong spring. It's about all my arthritic fingers can do to open the breech and put in the magazine. It takes force to do that.

The only loading data with any reported pressures are found in Sharpe's 1937 Complete Guide to Handloading. Hercules recommended 24.7 grains of 2400 with a 200 grain jacketed bullet. This generates a reported 50,000 psi. With the 250 grain bullet, 23.3 grains of 2400 generates the same pressure. Those loads may generate 50,000 psi, but they do not generate enough force to reliably operate the action. The breech block is not blown back far enough to eject the case, there is unburned powder in the residue in the action, and the rifle is inoperable until the action is worked by hand and the fired case extracted. If you stand behind and to starboard of the shooter firing these loads, you can see fire in the chamber when the breech block opens.

When I switched to IMR 4227 powder, the action operates as designed. DuPont did not provide pressure data but recommended the following: 31.0 grains approximate factory ballistics with the 200 grain bullet and 27.5 grains approximates the factory load with the 250 grain bullet. With either load, hot empty cases come flying out of the action. The recoil spring is compressed far enough to load the next cartridge from the magazine and the rifle operates as intended. If you stand behind and to the right of the shooter, you do not see fire in the chamber.

The loads of 2400 may well develop the reported pressure in a test rifle with a fixed breech. Campbell's book shows a High Wall used by Winchester to develop this cartridge. But the powder burns too slowly to impart sufficient force to operate the action. IMR 4227 burns faster and provides the force necessary to operate the action.

Richard

Methinks you may have it backwards, 4227 is slower than 2400, especially these days when 2400 is even faster than it was 30 years ago. You're right about the burning rate affecting the blowback action, the slower powder gives a slower & thus longer-acting shove necessary to keep the heavy breechblock moving back far enough to cycle the action. It's not an exact apples-to-apples comparison but it does point out some of the effect of a different burning rate. The 2400 slap doesn't last long enough to move the block far enough but I'll bet that repeated use of the fast 2400 load would eventually batter out the breech face while the slower 4227 load would not be as damaging. Again, JMO.
Regards, Joe

Corrections acknowledged & accepted, Joe. Thanks. I think this discussion has demonstrated that it is force and the rate of application of that force (quick slap vs sustained shove) that causes things to go amiss with our elderly rifles.

But I'm still unclear about the requirements for complete burning. The fast slap from 2400 is enough to push the case (1.5" long) from the chamber. When that happens, a non-blinking observer can see fire. If you can see the fire, the operating pressure must be close to atmospheric. But the action is then sprinkled with unburned grains of 2400. What is happening to cause that?

BTW, if you have one of these beasts, the 401 ammunition with Cabella's name on the label is apparently loaded with 2400. The stuff from Buffalo appears to be loaded with 4227.

The reason that you see unburned grains of 2400 is that it's 2400 (G). Sorry about that (VBG)! No seriously, 2400 just plain doesn't burn cleanly, not 100%. I've been using it since the '60s in lots of loads for lots of calibers, still got maybe a pound of my last caddy left, time to order some more. It's a wonderful powder but it WILL leave lots of unburned grains even with the heaviest loads.
Regards, Joe