Am loading up some .223 for AR. Been reading all about bullet setback and crimping vs not crimping. Here is what I did: I loaded a 55gr. JHPB dummy round to 2.250. Loaded it into a magazine and chambered it, ejected it 5 times. Each time the bullet did not setback, it increased the COL by .001 each time. I crimped the round, it is non cannelure bullet (bunch of people who said they crimp used non C bullets). After chambering this round once and ejecting it I measured it and the COL increased by .005. I thought this interesting.