First day I had my KPF upper with Ceiner kit installed I blew through 2500 rounds in autofire in my M16. Ammo cost = about $45. If I were shooting .223, the bill would have been hideous. Even in semi, I am REALLY enjoying my rimfire kit and the uppers I had built are tack drivers.
If you can't bumpfire the Ceiner kit, that is truly a shame. I look forward to try to bumpfire just about everything I can. I have a Mini-14 that I legally modded to fire when the trigger is released as well as pulled, I wonder if that will double my ROF when bumpfiring, or make it unsuitable to try and cycle?
It's probably rude to bumpfire a friend's firearm without telling him, but I love the look on their face. When I bumpfired Arcticbear's short barrelled AR, he was behind a vehicle, sight blocked so he couldn't see what I was doing, and his first thought was "Oh great, what just broke in my AR???" Classic!