I've built maybe 8 of them in the past. I didn't have any issues at all with them and they shot very well. The gas port needs to be properly sized, usually running .005" or more smaller than the 5.56's. I worked my way up from .070" or so and if I remember right got great function in the high .070's/very low .080's. Mid-length system with 18" bbl was smaller yet. Accuracy was excellent and the coyote hunters I built them for were very happy with them.