New Brass VS. Once Fired Brass Velocity


Well-Known Member
Feb 4, 2009
I should know the answer to this but can not find my data.

How much of a difference will you get with new unfired brass compared to using the same brass once it has been fire formed to your chamber? All other load components are the same.

Hope this makes sense.
Others will be able to answer this better than I can but I will give you a couple examples that I have had. New brass in my 308 only stretches the shoulder .002 and when I FL size it I push the shoulder back .0015 to .002 so typically I haven't seen changes in velocity. On the other hand, I have a factory 700 in 300 WM and the shoulders stretch .014 when fireforming. I also FL size this bumping the shoulder .001-.002 and if using the same recipe, the velocity really falls off due to the increased case capacity.
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