Out of spec or tolerance stack up?

[hanschien]

I recently ordered and received from Aero Precision two assembled upper receivers in FDE for "future builds" because they were on sale. I tried to test fit a standard barrel nut from BCM that we'll call example FDE-1. Hand tightening with grease was met with slight resistance at a few places with some of the coating shedding off, nothing out of the ordinary. I then did the same to example FDE-2 without issues.

I then decided to move a Geissele hand guard (MK4) from a previous build that also used a cerakoted Aero receiver (titanium). This time the Geissele proprietary barrel nut hit a wall half way on FDE-1 and I couldn't hand tighten any further. Worried that I might have crossed threads, I backed out the nut. I tried again and met resistance half way. With FDE-2, I was not able to hand tighten the Geissele nut at all.

So do I have something out of spec?

1. Standard barrel nut easily hand tightens on all three uppers
2. Geissele easily works on the titanium, halfway on FDE-1, and not at all on FDE2

[GH41]

Your problem is the cerakote and tight end of spec Geissele nut. You need one of these. http://www.midwayusa.com/product/699...8-thread-ar-15