The original set up was a PTFE washer backed with a neoprene ring.
I believe later aftermarket replacements are polyurethane. See reference in the Knibbs ad:
http://www.airgunspares.com/store/pr...-Part-No.-V10/
I have only seen polyurethane used on these, as supplied by spares suppliers.
Baz
BE AN INDEPENDENT THINKER, DON'T FOLLOW THE CROWD
The original set up was a PTFE washer backed with a neoprene ring.
I believe later aftermarket replacements are polyurethane. See reference in the Knibbs ad:
http://www.airgunspares.com/store/pr...-Part-No.-V10/
Yes, its because PTFE is a malleable material that deforms, they probably were quite ineffective early on in their lives. The properties of polyurethane are 100% better for piston seals. I think I have only removed 2 PTFE seals from rifles in the last 25 years. Not sure what the blue material is they used in old Webley pistols, that looks a bit like PTFE. Also not very impressive.
Baz
BE AN INDEPENDENT THINKER, DON'T FOLLOW THE CROWD