Failure to stop drills are usually a hammer pair to the chest followed by an aimed shot to head or pelvis. I was taught to aim for the t-box on the head to most easily penetrate the skull. A shot to the pelvis is intended to shatter or break the pelvic bone to immobilize an attacker.
I was issued an Otis kit with my M16A4, and have acquired a few extra kits over time. I like the little guy but basically supplanted the parts from it into the rest of my cleaning gear.
Looks nice, but why no rail covers? I personally am not a fan of the cheese grater that is a rail system without some covers (but I like having rails). Other than my personal tastes I like what you built quite a bit.
My AR seems to like it better than most other stuff I've put through it.
And I have used XM855 at hap and they didn't ask what kind of ammunition it was.