Outstanding ! Just finished a new rifle length build, 120 rounds of steel cased Russian surplus without issue. No stuck cases, No feeding issues, Chucked shells in a pile at the 4o'clock position. Accuracy is good for flip up sights. I've heard a lot of negative issues about this cartridge, but still wanted to build one. Grid Defense " Nailed It " with this upper. With a rifle length stock/buffer set up, the gas system looks to be Spot On !! I would recommend this, if someone is looking for a 7.62x39 upper.