Excellent barrel - Aero Precision M4E1 Enhanced 18in .223 Wylde Fluted Complete Upper Receiver with Flash Hider

Let me address the short stroke issues that some are having. The 18" barrel with a rifle gas system shortens the dwell time considerably. This is the time from when the bullet passes the gas port to when it exits the barrel. With a rifle stock and buffer tube, this isn't usually a problem, but when you add the carbine stock with a shorter, stiffer spring than a rifle tube, it is just enough to keep it from cycling properly. The best remedy is to use a rifle stock, another option is to use the shortest, lowest coil count carbine spring and see if that will work. Otherwise, to use the carbine stock, you will probably need to open the gas port to about .100"-.103". Normally it is about .093". It should cycle reliably then.