Well, I can tell you what NOT to buy. I bought a DPMS bull barrel upper and it ran okay but was too heavy for plinking and I decided I wanted iron sights. Sold it when Bushmaster came out with theirs and bought a Bushy. It was a jamomatic. Sent it in to Bushmaster and it came back still jamming. Sold it at a great loss (with appropriate warnings about jamming) and bought a DPMS A2 upper. It was a jamomatic! Sent it into DPMS and they replaced the extractors. Sold it as soon as it came back (again at a loss) and gave up on .22 uppers. YMMV!