I've loaded for the 300 win mag since 1981 - never crimped a round. I think I have over 2,000 rounds thru the gun to date. But I had a friend who felt it was necessary, only used Hornady bullets with a cannelure. He might have had some older dies that didn't squeeze down his necks quite tight enough - don't know for sure. If I did start crimping I'd get the Lee Factory crimp. Use them on my 30-30, 348, 357, 41 and they work very well.