I have been considering utilizing a suppressor with a short barreled AR upper to meet thte 16 inch requirement. This of course would mean the can was permanently fixed to the barrel by pinning it in place. This seems like a viable solution to a number of problems relating to SBR use as a 10.5" PWS upper with a 6" suppressor provides a handy and somewhat quiet 16.5 rifle. Especially if a quad rail float tube that covers some of the suppressor can be located. Thoughts?