My ciener has been nearly flawless. I now have it in an upper built with a 1-16 twist barrel off of a cz 22 hornet that was rechambered to 223. The accuracy is phenominal, way better than I expected. It also shot really well in my 1-9 carbine, but not so well in a 1-8 twist barrel. The ammo you shoot makes a big difference in accuracy also. But it does function with everything from hyper velocity to subsonics perfectly. Two friends with the cmmg units have had the same results. But as always, ymmv.