30BR Post Fire Form Length

A

abintx

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Lost my notes in a computer conversion. On average, how many thousandths does a 30BR case shrink upon fire forming? What's your experience? Thanks, Art :)
 
I'm guessing you are talking the CoW method? If so, my experience has been in the neighbor hood of .003. Starting from 1.5530 and finishing up around 1.55ish.

If needed, mandreled up brass goes from 1.5530 to 1.5240 prior to fire forming.
 
Steelhead1 said:
After fire forming ballpark? 1.520! Trim to 1.500.
Click to expand...

Mine measure 1.518" to 1.520" after necking up.

I measure cases out of the box, after pushing the shoulders back, after necking up, and after fire forming. It's interesting to watch what happens. I guess I'm more curious. :)
 
Last edited by a moderator:
Steelhead1 said:
After fire forming ballpark 1.520! Trim to 1.500.
Click to expand...

Depends on the reamer. Some of us are using a reamer that has a 50 thou long neck to make use of the extra neck that you get when formed by rattling a 6mm bullet down a dedicated fire-forming barrel.
 
Thanks SG, I have PTG Robinette grind, after fire form I am seeing 1.522-1.524, then trimming to 1.510. Long process, I am currently making 100 pieces of brass,!
 
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