We've had this in the grey matter storage for years but got around to testing it today. Previously we've moved away from seals as they appear to be quite unstable across temperature changes. We moved to o-rings which improved matters but recently I felt there could be more to be had. So after researching good and bad materials for temperature change we've finally found one which is about the same as aluminium and we can machine really nicely into a ring to fit exactly how we like. We didn't think it would be this simple but this is doing about 10 fps more than the o-ring at 760 fps on a 22mm 155g full skirted piston with about 1mm of preload and settled down instantly. A hint of Krtox on the piston and moly everywhere else. It's a long stroke because that's the flavour I prefer. It actually feels faster now though so I might slow it down some more. Few photos... the one with the high snatched shot is at 28 yards, and the other with 5 was at 55... i'll see what she's like over the next few weeks while I tweak the stock to fit betterer.