Looking at different Colt M16/AR15 bolts and noticed that some have a more rounded part to the rear of the locking lugs, as well as a small diagonal cut behind the lug, on the bolt body. This was done on earlier bolts? This for stress relief?
Later Colt bolts, as well as BM bolts I have, show a square lug profile, and no diagonal cuts on the bolt body.
Why the change? Is one type stronger than the other?