I gave this some thought and have two solutions. 1st would be to get the barrel Freaked to the depth of the bevel. Simple yes as well as obvious. 2nd was an idea gleaned from a barrel I saw on E-bay that used an external O-ring as a détente. The way it was done was a groove was machined around the out side of the barrel and the groove was cut all the way through on opposing sides or top and bottom. This aloud the O-ring to actually go into the barrel. Well that got me thinking of just machining the barrel about an inch from the body but not so far as the pump comes any way near it. With a tight O-ring going into the barrel it would keep the Freak in tight. Feyd...........Heres a picture.