09-17-2022, 12:29 AM
OP, you are going to need to tweak your load when you move to fired brass since the case volume of virgin brass will be lower than that of your fired and then resized brass. When I switched from a Hornady die to the RCBS Small Base die (which will have the dimensions of virgin brass), I think I ended up using 0.3 gr less powder and ended up with slightly lower velocity. The internal ballistics do change a bit.
You can see/feel the difference with your virgin converted brass. Since the brass flows down the shoulder towards the body when you neck down, there is a slight bulge at the base of the shoulder where it meets the case body. Whatever slight bulge there is will be the difference between the dimension of the virgin case body and what it will be after you fire and resize it.
I used to subscribe to fireforming virgin brass, but no longer do with component costs and availability. When I had to buy new 6.5CM brass and switched brands, I developed a load, shot 2 PRS matches with virgin brass and then tweaked it a few tenths. In addition to component costs, it didn't seem prudent to use 20% of a $500 barrel's life (300 of 2500) for fireforming either.
You can see/feel the difference with your virgin converted brass. Since the brass flows down the shoulder towards the body when you neck down, there is a slight bulge at the base of the shoulder where it meets the case body. Whatever slight bulge there is will be the difference between the dimension of the virgin case body and what it will be after you fire and resize it.
I used to subscribe to fireforming virgin brass, but no longer do with component costs and availability. When I had to buy new 6.5CM brass and switched brands, I developed a load, shot 2 PRS matches with virgin brass and then tweaked it a few tenths. In addition to component costs, it didn't seem prudent to use 20% of a $500 barrel's life (300 of 2500) for fireforming either.
#FJB