[SDC]

I've fired a "Hushpower"-converted single-shot that was laid out the way you describe (with an expansion chamber that slips over a ported barrel and unscrews to allow cleaning) and it worked really well, except that the outer body was made of aluminium and it sort of "rang" when you fired a shot. They've got a page at http://www.saddleryandgunroom.co.uk/..._Hushpower.htm which shows the way their designs are laid out.