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

[felix gunner]

I have one of those boxes of multiples sizes and the only way to get something to fit (and actually be insertable) was to sit two thin ones side by side in the groove - it worked OKish but as I say they are pretty nicked after not many shots.

IIRC Bruce states that the Senior showed an increase in power over the MK I partly due to the PB ring (as over time the leather washer was compressed by impact) but my MK I puts out 3.2 ft lbs and runs beautifully with a very old cup washer.

Bruce also states that the piston on the Senior was 1/10" shorter for slightly more cylinder volume but more importantly was internally 0.4" less deep to give more spring compression. The MK II Target used two piston rings so maybe this would have worked better.

I know adding a leather washer will reduce cylinder volume slightly but would rather try this first than mill the piston and if I could get my Senior to match my MK I and (reliably and consistently) make over 3 ft lbs that would be desirable.

In the pic below you can see the piston has been milled back.

I would have thought that rather than using a leather inner washer (as on MK I) - that the delrin/polythene inner as on a Junior II would be better and stop the cup washer compressing if it impacted the end of the cylinder? (Interesting stuff on all this and how Webley tried alternatives to the PB ring etc on p88 of Bruce.)