collapsed cases in a 7mmRUM?????

[JustC]

I have heard of this happening with this caliber,..and last night saw it for myself. The load was 94gr of retumbo behind a 162gr a-max in a sendero SF. The same load printed ~.5moa last weekend with a temperatire difference of no more than 10 degrees. Lst night on a hunt,..a buddy fired one more and the case came out with 2 collapse marks just under the body/shoulder junction 180 degrees apart. The barrel was completely clean and dried,..the chamber was dried, and the bullets are at the lands. Anyone have any idea what causes this in this caliber?

 

[*WyoWhisper*]

sometimes if you have and case lube or foreign substance on the case it will do this... I have had too much case lube on a case already and it has "dimpled" the case..

 

[dbhostler]

I have the same rifle in the same cal. and the same problem when I first began loading for it. The problem is the bullet is exiting the neck before the pressure builds enough to seal the neck. Gasses are passing buy the neck and indenting the case. The solution is to seat the bullet deeper into the case to give more time to build the kind of pressure needed to expand the case enough to seal. You should also be using a mag. primer with this case if you're not already doing this. Let us know if this fixes the problem. There are a couple of other things you can do too, like increasing the neck tension.
db

[ 03-07-2004: Message edited by: dbhostler ]

 

[JustC]

We are using an RCBS FL die set and retumbo with 162gr a-max pills. I am thinking you are on to the same conclusion I am (not enough pressure build in enough time) I will see what we can do to increase the neck tension.

Ric,...I made sure he patched the kroil from the tube and mopped the bore,....but I will check on the case lube idea as he may have left some on the brass.

Thanks guys.