View Single Post
Old March 22, 2013, 07:54 AM   #4
SL1
Senior Member
 
Join Date: November 8, 2007
Posts: 2,001
When making .30 Herret cases for my Contender, I have found that they still shrink in length when fired for the first time, so long as I use modest-pressure loads for fire-forming. The cases are already sized so that the shoulder produces the "just closes easily" type fit in the chamber. But, the Contender break-open action is somewhat "springy" (especially if it isn't a G2 frame). So, after each firing, the shoulder always gets pushed foreward enough to require set-back during resizing for the proper fit.

The reason that the cases grow on the first firing is that shoulders and body need to be blown-out for minimum taper of the body, and the brass has to come from somewhere. If the case does not slip a little in the neck area then the extra brass comes from stretcing the body down near the case head where it does not expand enough to grip the chamber wall. That is the area where stretching reduces case life by starting case head separation.
So, I ususally fire-form with unoiled cases and modest loads to get the most reloads out of my cases.

Loss of length on the first firing is about 0.008" to 0.010" when forming from .30-30 brass. I usually allow for this when cutting-down my .30-30 cases, because a cast of my chamber revealed that it is long enough to accomodate somewhat over-length brass. Subsequent firings with full-power loads typically increase case length by about 0.002" to 0.004" per firing. (Contenders are notorious for short brass life with bottlenecked cases and stiff loads.)

SL1
SL1 is offline  
 
Page generated in 0.03317 seconds with 8 queries