The heart of the AR-15 is its simple, robust direct-impingement gas system. But if the gas ain't flowin' right, your rifle will malfunction. Brownells Gun Techs Caleb and Steve share some tips for figuring out what's wrong. First, determine if your AR is over-gassed or under-gassed. Is too much gas flowing or not enough? The key is to watch how your rifle ejects spent shells. On a properly functioning AR-15, they should zip out of the ejection port at about 3 to 5 o'clock. If the shells eject FORWARD, your rifle is OVER-GASSED because the shell isn't clearing the ejection port before the bolt closes again. Easiest solution for over-gassing: install an adjustable gas block and dial back the gas flow. (Alternate fix: try a heavier buffer.)
Short-cycling or not fully ejecting spent casings is usually a sign of being UNDER-GASSED. Make sure the gas block fits snug on the barrel's gas journal and the gas tube fits tightly into the gas block. If either is loose, gas will leak and there won't be enough left in the system to cycle the action properly. A loose gas key on the carrier will also cause a loss of gas pressure. This is why you always want the screws on the gas key tightened down and "properly staked." And if the gas tube isn't correctly aligned with the gas key, it can wear the key over time, causing another gas leak. Finally, check for worn out gas rings on the bolt. Caleb shows us his handy trick for determining if the gas rings are worn. If these fixes don't solve your gas system problem, we'll be flabbergas.... ted!