I'm not saying there are not FFL's that will not do it, but every one I am familiar with, to include standing behind the counter for at times, will only book a AR in from a individual as either a rifle or a pistol, they only book them as others from the distributors, I also have not seen too many people trying to sell used stripped lowers through FFL's around here, Typically those are armslist sales conducted in Walmart parking lots.....