Wasn't that another Brocock? A converted Lee Enfield rifle that used air cartridges and NATO bullets. I seem to remember they were all the rage when a TV programme featured them shooting (shaken up) tins of Coke which caused them to explode on hitting.
I think they also converted a full bore rifle - the Parker Hale 2000. Im sure someone will be along who knows a lot more than I about these guns.
ATB
Ian
Founder & ex secretary of Rivington Riflemen.
www.rivington-riflemen.uk