I don't crimp at all for the 300 Blk, or anything else I fire in an AR for that matter. It isn't needed. With some jacketed bullets that have a cannelure, it probably won't hurt anything if you want to crimp, other than case mouths cracking sooner, but it won't gain you much of anything either as long as neck tension is good. With cast bullets, applying a heavy crimp can cause leading and accuracy issues.
I do use a Lee FCD to remove the flare in the case mouth when loading cast bullets, but don't do any more than just straighten out the neck.
