? wet chamber = case separarion ?

[texasmac]

Hi Ed,

I tend to agree with you about the frictional affect of black powder, but will add that case splitting or separation is definitely possible in modern high-power smokeless ammo in a SAAMI spec'd chamber. I ran into it in a Rem. 700 in .30-06 and, after verifying the chamber specs, conducted an experiment to identify the cause. It turned out that, although the headspace was quite small (only 0.002"), after full-length resizing and firing the case 12 to 13 times, the accumulated affect resulted in the case splitting in front of the thick section ahead of the rim. In this situation, slightly lubricating the chamber would have reduced the possibility of splitting since it would have allowed most or all of the case to move back slightly, not only the rim. Of course it would also increase pressure on the bolt.

Wayne

[EDG]

Hi Wayne,
I agree that you can separate a bottle neck smokeless case in the that manner or with gross headspace with fewer shots. I do not think the powder grabbing the case mouth plays a big role as it does with BP.

EDG

[SlamFire1]

Of course it would also increase pressure on the bolt.

Yes you will increase the load on the bolt, but as long as your loads are within SAAMI specs, which is the pressure/load level the action was designed to support, nothing will happen.

If you put 500 lbs in the back of a ¼ ton truck nothing evil is going to happen, outside of increased gas consumption and a longer braking distance, because the truck was designed to carry 500 lbs. You put 1000 lbs in the back of your ¼ ton truck, you will acclerate wear on the springs, struts, ball joints. At some bed load the tires will pop and the axles bend.

Trucks and actions are designed to carry loads. For an action, if you don’t exceed the design loads you will get a normal service life out of the thing.

Actions are designed assuming zero cartridge case friction. However it may be darn near impossible to ever reach design loads with SAAMI spec cartridges as there is always case friction.

You can see this in the analysis conducted by Varmit Al:

http://www.varmintal.com/a243z.htm

Only when you reach physically impossible low levels of friction is there any issue with a 243 Winchester. The computer shows case head issues with physically impossible levels of friction. But this is only science fiction as you cannot ever get the coefficient of friction that low.

What he does show is with smokeless cases and oiled cases the case head is not stretched. Peening will occurr if there is too much headspace, but peening will occur clean chamber or wet. Low friction cases will accelerate peening. Because peening is always bad this provides another reason to control your headspace.

I generally push back my case shoulders .003", probably some are pushed back more.

Smokeless propellants are operating at 50,000 psia. I have no idea the maximum pressure you can get out of blackpowder, is 20,000 psia the max?

I assume with the black powder cases the case head obdurates and no gas release occurs, but maybe the inside pressure is not enough to support the case against the inside friction of the bullet.