Re the Ptfe washer not returning to shape---fair enough. I assume they are ok on the cadet and Major becasue the block slopes? I would have thought that any restriction of air flow would up compression ratio? made leather washers for small Webley and Diana rifles, where the hole in the washer closes up to the point where the gun wont fire (although clearing the hole a few times until the seal settles works). assume that the compression had increased to the point that the piston could not force the air out? I think (offhand) that compression ratio (on an engine) is the volume of the cylinder/volume of the head so a 500cc cylinder with a 50cc head = 10 to 1 compression? On a webley, as you could consider that the seal is about 1/4 inch thick, any reduction in the size of the hole in it must reduce volume and therefore up compression? Obviously with a thinner washer, less of an effect.