Yes, definitely possible, and available; I've fired a Hushpower single-shot, and it was an interesting experience; the expansion chamber ran basically the whole length of the barrel, so there were 1/4" ports the whole way, with threaded discs for mounting the outer tube welded onto the barrel (you could unscrew the outer tube for cleaning/maintenance). There were a couple of odd things about this set-up; one, it had a weird sort of "thump-riiiinnnnng" sound when it was fired, because the outer tube acted like a bell when the pressure hit it. Two, there was enough residual pressure inside the expansion chamber that it tried to fold the pie-crimp on the shells back in, at least 3/4s of the way.