After twice fireing some cases that were resently made to fit the second 7.62 X 41 I found that they all had shortened between .010"to .015". In all my years of fireforming I never realized that this happens. Thinking about it, however, it is definitely understandable. Anyone else surprised? roger

well, i won't tell you that you ight have over shortned them when they were trimmed, first or most immediate time..

but if they are 41MM long BEFORE firing , and anything like improved from after, than of course they are now corret in all other dimensions...

i trim the AR cases to 2.65 if i die form them, then fireform and trim to 2.55, for thr rumbased ones

quote:

Originally posted by jeffeosso:
well, I won't tell you that you ight have over shortned them when they were trimmed, first or most immediate time..

Prior to loading and fire forming the cases measured nominally 1.618". They now measure between 1.604" to 1.615".

Is it so hard to believe that the brass necks can donate to the forming of the body and shoulder? roger

Anytime you sharpen a shoulder or expand it in diameter to reduce the taper of the cartridge body, the cartridge usually ends up being shortened as the brass has to come from somewhere. Even if it's just that the chamber is a little larger than the brass, that first firing will shorten the brass as it expands to fit the chamber more exactly.

quote:

Originally posted by CMcDermott:
Anytime you sharpen a shoulder or expand it in diameter to reduce the taper of the cartridge body, the cartridge usually ends up being shortened as the brass has to come from somewhere. Even if it's just that the chamber is a little larger than the brass, that first firing will shorten the brass as it expands to fit the chamber more exactly.

I see it the same way, now, never gave it much thought before.

I use to shoot trap in Grand Junction ,late 60s early 70s with a Dwayne McDermott. Any relation? roger

quote:

Originally posted by CMcDermott:
Anytime you sharpen a shoulder or expand it in diameter to reduce the taper of the cartridge body, the cartridge usually ends up being shortened

I've observed this a couple of when forming 'cats.

I do suscribe to the notion that as you "true up" or "blow out" the body/shoulder and shoulder/neck junctures, your case shortens.

Think about it as a piece of string laid alond the surface, being fixed at the case head. As these curves straighten into crisp angle points, the path becomes longer, but not the OAL - it must shrink.

quote:

Originally posted by MuskegMan:
[QUOTE]Originally posted by CMcDermott:
Think about it as a piece of string laid alond the surface, being fixed at the case head. As these curves straighten into crisp angle points, the path becomes longer, but not the OAL - it must shrink.

Nice analogy roger