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Old December 2, 2009, 11:11 PM   #1
Senior Member
Join Date: September 8, 2008
Location: NW Wash State
Posts: 216
More on headspace - why does gun shoot better?

my CZ 527 Varmit .223 seems to shoot a very consistent 5 round group when I resize the case to -.008" to -.010" shoulder length.
Using the Precision Mic Gage a fireformed round from afore mentioned rifle is .003" to .004" below the "0" mark on the gage. I normally resize cases to .006" below "0", they chamber and shoot nicely.

I didnt realize the die was out of adjustment and resized about 50 military brass (all brass is LC) to .010" to .012" below the "0" mark on gage.
I loaded 5 rounds to "fireform" them and was amazed at the improvement in accuracy.
All other factors were the same. Powder, primer, OAL (use Hornady's gage).
Twice more I have gone to the range with 5 batchs of 5 ea. test rounds in small zip lok bags. 2 bags with the shortened brass and 3 bags with brass resized to fit my chamber. Each time the bags of 5 rounds were all shot using a blind method where I did not know which bag was which. Both times the shortened cases were more consistent and accurate (1/4" minus) then the longer ones (3/4" minus).
Does anyone have an idea why this is happening?
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