For a while I’ve been shooting o-rings and they’ve seemed stable but only in relatively mild conditions. So we decided to revisit piston rings, something we’d mulled over a few years back along with a seal/ring free design (which still made 725 FPS which we thought was pants) and another ring design we’ve yet to play with. The easy fix was to use the channel we had in the head for the o-ring and we duly dropped in a ring to fit and voila it worked. Except I didn’t like the feel. So we made one out of delrin which sealed tighter and felt better. All good, plenty of power, job done and I moved back to making the stock fit better. As we’ve had a cold snap and some of the stock work was complete we decided to test the rifle in the cold. Leaving it out last night and measuring the temp we had readings of -5 to -7 on the gun. Wearing the same gear as the previous day when I’d zero’d to the click at 25 yds we braved the elements and shot the same distance. We saw a definite rise in the POI from warm and the chrono was also indicating a significant increase from when we last chronod it. The cocking action also felt like it had a lot less friction. So we got the mic out for some measuring and selected one of our carbon rings that was similar in size and fitted that and left her to cool. Over the chrono the power was the same, and we were pleased to see that when the gun was warmed to close to 20 degrees the gun was the same speed. This would suggest that we might have found the tolerance for the fit and the material to do it with but it’s early days. What we are pretty convinced by is that any material softer than delrin is probably not going to work and you’re looking at tolerances of 1/100th mm if you want consistency. I think I’m going to have to leave feel aside for the moment and just rest consistency further for a bit. The hope is I’ll be able to bake the rifle during these cold snaps and get a wide range of testing done. If this doesn’t work then might just go to the seal less design and tune the feel other ways.