I looked at a AA 50 BW upper about 15 or 20 years ago. I Bought a dummy round key chain and a 20 round box of factory 400 grain FMJ ammo. The USCG adopted the 50 BW and use the 400 grain FMJ as a "Breaching" round on drug interdiction searches.

The 500 BW is like all modern (post 1968) 50 cal cartridges and uses the .500" diameter and not the old 50-110's .510", or the British .505"! I have a couple hundred Speer 325 grain SHP's left over from selling my 50AE, I still keel thinking about getting a 50 BW upper (but the 450 Bushmaster is soooo much more affordable!)

Ivan