300 Norma Mag help!

[marzo2]

So I have brand new Lapua brass, Forster FL die, Hornady (0.420) and Whidden (0.450) bump comparator.

I lube the case, adjust the sizing die as usual (when the ram is up, it touch the die). Run a brass through the die... same mesure as it was. So I screw the die in 1/4 turn, run it again, same mesure.

What is happening? Could it be that the brass are under size?

I dont have a fired case or other brass to compare

 

[pabrousseau]

cases are probably slightly smaller than your sizing die which is no problem. you will need fully fire formed brass to measure your chamber length and then adjust sizer for proper shoulder setback .