my AC556F is sitting at the dealers waiting for the approved form 4 but I got a chance to install and play with the ciener kit I bought from Kevin along with his mags. WOW! more fun then a barrel of monkeys. I shot over 250 rounds in single (not alot) 3shot burst (some) and full (a lot). all flawlessly. I used Remmington hi velosity brass washed 40 gr solids. BTW this is the gun I traded for my Sterling and honestly although the Sterling was super, I'm very happy I made the trade. Best to all, JB