I had an AR-10 "Infantry Rifle" maybe 13 (or more) years ago. It was the 20", fixed carry handle model. Wouldn't cycle for shit. Sent it back to Armalite and eventually talked to one of their armorers. He said the gun was designed to run exclusively with 168gr Match ammo! I was like "WTF?" So I'm supposed to buy high-end 168gr OTM ammo for this thing just for range plinking? I don't think so. Should be able to cycle 147gr FMJ fodder (not crappy steel-cased stuff, but Port surplus or Winnie White Box). Finally ended up putting an M-16 rifle spring in it instead of the AR-10 one and it ran fine. Go figure. I never fully trusted it after that and traded it in for another rifle.