300 221 Whisper
I know I will catch noise about this but had feed problem on 300 221 whisper. On new brass formed from 223 it would not lock in, ( this is a new barrel). Once fire formed they worked great. Checked with caliper and die was not setting shoulder back enough by 10 thous. I put the die in lath and removed 20th off it and feed was good. Short throught on new barrel. This is a ar platform.