Yes, Bushy is now making a new model M4 with a piston. Expensive but yet the bolt and carrier stay very clean ! Prob. is that the gas "plug" on the block is stuck. Going to send it to Bushy as I would hate to damage anything by trying to force plug out. And so new, most gunsmiths probably are not exposed to the model yet. So, warranty is a good thing this time..
Gunpowder Addict For 40 Years Now