Free float main purpose is to keep any pressure off barrel for the sake of accuracy. Side bonus is being able to run a handguard longer than your gas system. You can hang stuff off of non floated handguards just as well as floated. There was a article a while back where a guy showed some pretty big POI changes with non floated handguards and a bipod. Obviously wouldn't be as bad with a piston since the weight of the gun isn't resting on the end of the barrel, but I'd think it would have more affect then a gas block. Only reason I brought it up is because it seems it wouldn't be as good from a competition standpoint. I was just thinking out loud though. I have no experience, and no desire to own or build a piston AR. the system wasn't designed to work that way and its just different for the sake of being different for as I'm concerned. I have zero of the problems a piston is suppose to fix.