RE-A5SR Receiver Extension A lot of you are sleeping on what is arguably the better of the two A5 Receiver Extensions we offer, and we just made a whole bunch of them! Generally speaking, our most popular tube is our 7-Position RE-A5 (Receiver Extension – A5), but the one we are talking about today is our 6-Position RE-A5SR (Receiver Extension – A5 Short Rail). It’s the exact same length and depth as the 7-Position tube, and serves the same purpose – the difference between the two is the length of the indexing rail on the underside of the tube. The