The predecessor of those was the Jackal. Made by Sussex Armoury using as a main subcontractor the company that later was AA. From a very reliable source who worked there on a top secret project (cant be discussed due to secrecy agreements on an open internet forum) I got some information on the use O rings in the Jackal. JB said that after blacking and before assembly the cylinders were lightly honed using something called a Flexi-hone. These were brought in from the US and looked like bottle brushes with abrasive balls in the bristles. This removed any blacking and left a crosshatched finish. When checked for velocity some .22" Jackals went over the top and a quick production line fix was to ream the loading tap slightly oversize to drop velocity a little.