Fire forming and getting great groups????

[AWLEAPHART]

I was wanting some input on something I have read on the site over and over.
People posting about fire forming there 6br brass to BRX or Dasher ect, and getting small bug hole groups but after the brass is formed and the start load testing sometime don't group as good. I was wondering what make forming brass group so good?
Anthony

 

[bblackwell]

My opinion is that a new case has plenty of room for expansion and will center up in the chamber better when fired. I think there needs to be some space around the cartridge and not wedged in there so to speak. That's why I now bump my Dasher shoulders back .002 - .003 instead of just a half thou. .... I also use a Harrell's D4 die that sizes the .200 line back to about .469 . I feel that helps also.

 

[KMart]

my theory is that when fire forming, the expansion of the brass causes the peak pressure to take a little longer to happen. It is kind of like hitting the second or third node down from max.

That is all theory and what do I know?

 

[Terry O]

That's why I now bump my Dasher shoulders back .002 - .003 instead of just a half thou. .... I also use a Harrell's D4 die that sizes the .200 line back to about .469 . I feel that helps also.

Interesting observation. Can you expand on what type of improvements you achieved in reduced group size, pressure reduction, etc.

 

[bblackwell]

Interesting observation. Can you expand on what type of improvements you achieved in reduced group size, pressure reduction, etc.

When I first got the new Shiraz Norma Dasher brass , I loaded it up with 32.2 gr. Varget and 103 Vapor Trails. That load without any development shot 1-2 in. groups at 600 yds. (I got lucky).... That brass lacks about .002-.003 being fully formed out of the box. I could not replicate those groups with once fired cases even after lots of powder chg. and seating depth changes. The sizing die I was using was not sizing at the .200 line so I got a D4 die from Harrell's and it sized the case back a good .0015 at the base and shoulder. At that point I was able to really tune the load back to tight groups again.

I'm not saying that's anything revolutionary , it just worked for me.

 

[Terry]

Most fire form with a lighter load. Often the load is the key.

 

[comagutsa]

i used 30gr of 2208/varget and 105gr hybrids jammed into my 6BRX and got great groups at 100m all touching and about 2 to 3 inch groups at 500m/547y, (the 30gr is close to what i was using on my 6BR load)
i then used 32.5gr to just finish off FF cases and at 500m i got 4 rounds in 1.3inch group on 2 different rounds but stuffed the 5th shot on the 2 different rounds and ended up with 2.4 and 2.3 inch groups , cant wait to start load testing it