Okay, So I’ve been helping a friend build his AR-15 and everything has gone smoothly up until we went to drop the bolt carrier group into the rifle. Upon further examination, it appears to be some sort of issue with the gas tube and the carrier causing the BCG to remain about a 1/4" from completely entering the upper. We placed the BCG from my LMT MRP rifle into his gun and the carrier fit fine and worked properly as far as I could tell. Went to drop his BCG into my LMT and the same problem, it doesn’t fit. Then to really make things interesting the rifle was taken to a friend who has a recently purchase S&W M&P15…the BCG fits in his friend’s rifle and his friend’s BCG fits in the new build just fine.
Here are the Build Specs on the Rifle:
Mega Lower
Vltor VIS midlength upper
Vltor Gas Block + midlength gas tube
BCM 16" barrel
Young Manufacturing Bolt Carrier Group
Could be that his carrier key is out of spec or has something stuck in it.
Look closely at the gas tube making sure it’s straight and centered. Also try it with only the carrier no bolt, cam pin or firing pin. Sometimes with ‘builds’ it bolts not fitting correctly/smoothly into barrel extensions.
Get an allen wrench that fit the size of the gas key screws, loosen them, re-align, fit, insert the bcg, if it goes in already, then tight it fit and stake.
But before doing this, make sure the gas tube is not the problem.
Another vote for carrier key/gas tube alignment. If that is okay try lots of lube. Dry new parts seldom move against each other as well as broken in and/or well lubed parts do.
Looks like the issue was a misaligned carrier key. Thanks for the help, honestly would not have thought that a BCG would have come with a key misaligned but now it fits in both the new build and my LMT just fine.