Im using an adjustable gas key from Rubber City Armory on my fixed sight 16 J&T Distributing upper. This upper was way over gassed but I have no intention of ever using a suppressor on this upper. So after I adjusted the gas the upper has been 100% reliable. I needed another bolt carrier so I bought a stripped carrier from JSE Surplus and had bought the RCA adjustable carrier key from Right to Bear. The BC and carrier key were quite a bit cheaper than an adjustable gas BCG.
https://www.righttobear.com/rca-adjustab...y-1ad-gky/
https://www.righttobear.com/rca-adjustab...y-1ad-gky/