Sierra 69-grain Match Kings are very close in length to M855 Green Tip. M855A1s are close to Sierra 77-grain Match Kings in length. A1 groups much, much better than average Green Tip.
My teams have fired it through M16A2s, M16A4s, and M4A1s with some pretty impressive results. I never saw significant wear feeding it out of legacy standard GI 20- and 30-round magazines. It's been the issue ammo for the Army Rifle and Pistol Championships.
I'd pick it any day over Green Tip and M193 (unless I'm shooting it at my own steel targets -- they'll get torn up).
My kid drawing M855A1 at the Army Championships in March:
https://scontent-dfw5-1.xx.fbcdn.net...0c&oe=5D087DA8