Yes, the barrel adaptor is a bit loose, but i'm not sure that're the problem. I don't quite understand why the BT M16 APEX barrel only screws in about 1.5 times, whereas with the stock barrel, i remember is used to require about 5 turns, maybe more.

EDIT: Oh, i've noticed the little pull-back thing. Something's happening...
EDIT2: Right, now I think it's screwed in completely, but the sight post is still pacing 8 o'clock.

I only had 3 hours sleep last night, so i'm lacking problem-solving skills at the moment.

I still need a hand with this.