Danny45,

Consider picking up an RCBS precision mic chamber for the 300 Win Mag. It will tell you if your individual cartridge is in compliance versus SAAMI spec and if not then how many thousandths you are off by (in either direction). It will take into account the cartridge' s shoulder and belt as well. Be sure to mic the ones that work as well as the ones that don' t and note the difference in thousandths. At first blush, it sounds like it may be the die or the adjustment of the die.

Just on a hunch, before spending $$ or asking for refunds/exchanges, consider mounting the full length resize die in your old " one at a time" press, adjust it firmly and see if the problem persists. As stated above, borrowing someone else' s 300 win die and cross checking is a good move.

Best Regards
EKM