Converting the Webley Senior from a piston ring to a leather seal?

[bcham]

some one converted a senior to a c02 pistol.
https://forum.vintageairgunsgallery....l-john-walker/

[wild boar]

engines usually use 2 or more rings so that the gap is overlaped so i guess to be perfect you could make a couple of thinner rings on a lathe - it would be intresting to see if it makes much difference but it should seal very well

[ChasP]

I recently replaced the spring and breech seal in my Senior and it has increased the power but not dramatically. After reading the OP I measured the hole in the new rubber breech seal to be 3.5mm
With a 4.5mm barrel I would have thought this is a restriction but don't know enough about fluid dynamics - tempting to drill it out to 4.5mm but I'll do a bit of googling on transfer ports and breech seals!
I know what you mean about introducing plastic into a Senior - it doesn't seem right even using a rubber breech seal. I would be tempted to leave well alone and just get something else if you need more power. Any gains you get will be so minimal anyway. It is frustrating that the piston ring doesn't seal a bit better though - but I wonder if the stepped design seals much better under power - ie at slow speeds it isn't compressed against itself or the groove it rides in.