Re: 300RUM problems
I just did something very similar on another caliber. Just like has been mentioned, turned out I had the seating die screwed in too far.
I reset the die by first backing the die out so far there was no chance the cartridge mouth would touch the crimp shoulder inside the die.
I put a prepared case in the press and ran the ram all the way up.
Slowly screw the die into the press, you will definitely feel when the crimping shoulder in the die contacts the cartridge mouth.
Back the die off 1/8 to 1/4 turn and set the lock ring.
Adjust your bullet seating depth as required.
"Hell boys, I'd rather be hung by my friends instead of a bunch a damn strangers."