So recently I decided to grab a M5E1 18inch barrel complete upper from Aero directly. When it arrived I took it to the range and found the last round bho didnt work for the magpul lr/sr25 mags. Along with this it only cycled m80 ball any heavier grains it would not feed.
After some research I decided to take it apart and measure the diameter of the gas port on the barrel. Heres where the issues are.
1) the handguard screws were not torqued at all. Not even snug, I could have breathed on my t-bit and loosened them. No loctite no degreasing of the screws, nothing.
2) the gas block was not torqued down nor did it have the typical red loctite. Also the screws and the gas block threads were not degreased.
3) there is no dimple on the barrel to align the gas block and the gas port. So upon reinstall its just a guessing game.( I do not have a bore scope)
4) While the gas port measured in correctly to their specs, it is an incorrect spec. .089 was what they drilled but that is to small for an 18inch .308. You need a measurement of .093-.096.
5) barrel nut missaligned and the notches shaved down so the gas tube fits over the notches. WTF. See picture.
All said and done gas port was resized to .093 and passed a 2 round function test.( it was late) reassembled correctly and so far it works. Although I will need to take it apart at some port and dimple the barrel for the gas block.
My advice build your own ar 10 upper or buy once cry once and dish out the funds.