Last weekend I got a chance to shoot an upper I swapped one of these new receivers onto and I wanted to point out an observation I made. I had a Troy buis (BCM branded) and an Aimpoint PRO on the old upper and I moved them over to the new one to re-zero. The buis was previously zeroed about 6 clicks left of center. On the new upper the buis zeroed 4 clicks right of center. The PRO needed about 15 clicks in elevation to shift the group down and on target but no windage adjustment was needed. The optic adjustment sounds like a lot but I have no idea how far from mechanical zero it was when it was zeroed on the old upper. It may be closer to mechanical zero now than it was before.
I knew I'd have to re-zero but for some reason I never thought about how much uppers can vary. I'm pointing this out for the benefit of consideration the next time someone posts an issue with a canted fsb, weapon that won't zero, maxed out windage/elevation etc. In my mind it's easy to jump to the conclusion of the fsb being canted in those situations but it's obvious to me now that sight/zeroing issues can be attributed to other parts; most likely a combination of parts adding up to a problem. It's good to know BCM has taken the effort to produce dimensionally correct uppers when there are so many poorly made ones floating around.
Last edited by Eric D.; 02-26-14 at 19:55.
B.A.S. Mechanical Engineering Technology
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