Rock solid - Stern Defense AR-15 6 inch Assembled 9mm Upper Receiver w/ 8 inch MLOK Rail

Bought the upper with a mag well adapter (glock) and heavy buffer with a spring/spacer. Easy install took all of a ten minutes. Headed to the range the next day and put over 250 rounds through it. Fed it mostly federal and winchester (115 gr and 124 gr) FMJ and some 115 gr and 147gr hollow points. Did a couple of mixed mags of FMJs and HPs to see how it would run. Used multiple types of mags, 19s, 17s, 19x and glock happy sticks. Glad to report no issues at all. It just kept running. Put a razor UH-1 on top and was getting 3 inch to 5 inch groups at 50 yards. I didn't think that was too bad for the federal and winchester. Very pleased with the product.