I only crimp handgun rounds and levergun rounds for the most part. The reason for crimping handgun rounds is the obvious need for the round to develop a complete burn, and the reason for crimping levergun rounds is so that the gun doesnt push the bullet in when loading in the tube, or it being fed into the action. I have tried crimping some .270 and .243 with no added benefits as far as I could tell. But then again, if I can get a consistant 2" group at 100 yards I am happy.