As promised, a little detail on how this is going.

Having stripped the rifle, the following issues came to light: The spring was a very tight fit in the piston, and the guide was very loose in the spring. The leather piston washers retaining cup and washer had broken, allowing the washer to pull off over the retaining rivet.

The teens who were using it at the time continued shooting the rifle as they assumed they were just missing the target….! As a result the piston flying forward under spring pressure, mashed the washers, and cup into a firmly compressed and stuck mess in the end of the compression cylinder. After considering options to remove this (rodding it from the barrel end just pushed straight through), I made up a brass scraping blade in a rotary attachment for the drill. This removed the issue successfully.

Stuck crushed piston washer

Rotary scraper tool

Success!

The next issue was to choose between synthetic washer or leather. The synthetic one requires an adaptor, that increases piston length, reduces swept volume and robs the gun of power. I started off removing material from the front of the piston face and the synthetic washer adaptor, but underestimated the heat transfer which melted the seal (which I was using in a jig to hold the part for machining)! The seal is an unobtainable size, so I have removed more material from the piston face to further increase swept volume. Using the leather seal this should enable me to run a softer spring for the same power.

The loading tap is very stiff. I have lapped this in with  fine valve grinding paste (and cleaned thoroughly afterwards!) which has fixed this.

The bluing is very thin and discoloured. I cleaned up the compression cylinder as it was the worst area, polished with 1000g wire wool to remove surface corrosion, degreased with white spirit and cooked off residue of this with blow torch, and then applied Abbey bluing gel whilst still hot-ish. I am super pleased with the result!

Re-blued cylinder #1

Re-blued cylinder #2

Re-blued cylinder #3