Webley pistol questions

[Benelli B76]

Thought PTFE piston seals are supposed to be self sizing (to an extent) in as much as every time it slams into the end of the cylinder the seal is squeezed out to the size of the cylinder?

Edit: although this would rely on perfectly parallel cylinder walls...


Sure TR Robb used to sell slightly undersized PTFE piston seals with the instruction to dry fire until the seal fitted? (I may be wrong though?)

What is supposed to happen theory is not always found in practice after looking at a few hundred cases. The Webley is such a weak performer, I would say it does not have enough power to expand the piston head material by impact. Virtually all airgun manufacturers use polyurethane piston seals today. PTFE is used by a few people for replacements because it is a very easy material to machine. Polyurethane takes a bit of care and skill to machine, it is more suitable for moulding. I am continually changing PTFE capsule seals in air pistols. They are usually white and have squashed into an indentation well below the level of the piercer, causing a leak.

Baz

[vbull]

So would you use polyurethane as seal material in an old Webley pistol Baz ? If so what shore hardness rod do you think I should I look for to machine ?

[Benelli B76]

So would you use polyurethane as seal material in an old Webley pistol Baz ? If so what shore hardness rod do you think I should I look for to machine ?

Bob, I like 95 Shore A, the harder it is the easier to hold in any type of metal collet you may use in the chuck.

Baz

[DCL_dave]

What is supposed to happen theory is not always found in practice after looking at a few hundred cases. The Webley is such a weak performer, I would say it does not have enough power to expand the piston head material by impact. Virtually all airgun manufacturers use polyurethane piston seals today. PTFE is used by a few people for replacements because it is a very easy material to machine. Polyurethane takes a bit of care and skill to machine, it is more suitable for moulding. I am continually changing PTFE capsule seals in air pistols. They are usually white and have squashed into an indentation well below the level of the piercer, causing a leak.

Baz

Hi Baz,

Thanks for the info which seems plausible so I'll take your word for it because I have very little experience with PTFE...do know that PTFE is supposed to be a malleable material with no memory so, in theory at least, it seems like it should be ok as a piston seal material...

Bring back leather seals, thta's what I say!

[abellringer]

I may be wrong so if anyone knows for sure please advise. I was told many years ago when PTFE came into popular use in airguns, not to machine it as it could give off poisonous fumes?? I have machined it but with a fan nearby for safety. Advice please guys as my info is 70's dated.
abellringer

[Vic Thompson]

There might be some info here that will answer your question : https://www.theplasticshop.co.uk/pla...data-sheet.pdf,
but I've read elsewhere that machining it is ok and it's a "high temperature" or burning problem which isn't likely to experienced when normal machining methods are used.

However, I'd like a definitive answer too, so it's back to the Forum for more informed input, but as an aside dust extraction when machining anything is a sensible precaution for even the most benign of materials.

HTH, Vic Thompson.