The only way to time a carbine length gas system correctly - GUNTEC USA AR-15 Carbine Length Spiral Pigtail Gas Tube

If you don't already know, carbine length gas systems are improperly timed on a 14.5" barrel and even more so on 16" which leads to case head swipe, broken extractors, bolt breakage and needing rubber D rings put in the bolt to up extractor pressure. This product eliminates all that by lengthening the gas system to a point in which the chamber pressure is dropped to safe levels before bolt unlock, making the rifle more reliable and the operation smoother. I use this in a Colt 6920 and Daniel Defense M4, you can notice a night and day difference in the cycling and the rifles are far more reliable. Only downside is the tube holds more heat because of the design but this is only a problem if you're dumping mag after mag in a full auto, someone shooting semi auto will never get the tube hot enough for it to be a problem