Hi Phil, I have never done one, but I believe you need to make up a special tool for one part of the operation. I speak to John Bowkett quite often (he designed the Spitfire) and he says you must use well fitting Teflon seal replacement. Other people who have done these themselves use different seals that stop the leak but you can get erratic f.p.s. when you start shooting after the rifle has been standing, and it takes a few shots to settle down.

Baz