Piston inner washer material

[Ormicron]

I am looking for some material to turn up a piston support washer for a Britannia. I have purchased washer kits from TW Chambers and John Knibbs over the years, they have a green plastic washer. It looks like a material I used to buy many years ago named 'Murfeldt', some form of nylon, Polypropolene, Acetal? any ideas? if so where could I obtain?

Ormicron

[starling]

You could try here #bay item number:384613502752 and look at there other items

[steve medlock]

I often make them from Delrin without any problems.

Steve.

[TonyL]

For any engineering plastics and lots of useful information.


https://www.directplastics.co.uk/


Hope this helps.

[Ormicron]

Cheers for the info, will trey some Delrin.

Ormicron

[Benelli B76]

Yes, I agree with steve, Delrin should be fine if you really need a support washer. I just turned up a polyurethane piston seal to replace the leather. Put the power up as these rifles have quite a weak output.

Baz

[IMG][/IMG]

[Ormicron]

Must have a go at making one

Thanks for the heads up

[BC312]

Although green plastic doesn't look in keeping with the gun of that age, there are other colours. Using a plastic support washer is a much better way to preserve the gun especially if you recessed the screw hole so the screw sits below the plastic on the front, also if the leather washer protrudes higher past the support washer as so to cushion piston head even more so if the gun is fired without a pellet accidentally . I have seen so many chewed up screws and old fashion brass type cup support washers that have failed most of the time with bent screw ends when encountered past abuse of firing a gun with no pellet, it can happen to anyone, you cringe at the damage.

[evert]

The green plastic may be "oilon", an oil impregnated nylon?

I've used delrin with good results.

[Dave2345678]

[QUOTE=Ormicron;8256148]I am looking for some material to turn up a piston support washer for a Britannia. I have purchased washer kits from TW Chambers and John Knibbs over the years, they have a green plastic washer. It looks like a material I used to buy many years ago named 'Murfeldt', some form of nylon, Polypropolene, Acetal? any ideas? if so where could I obtain?

I would advise Nylon, which is what Chambers use. Maybe they use oil impregnated variety but Nylon 66 fine.
Nylon has high resistance to impact loads, which Delrin absolutely does not and will crack.
Often people choose Delrin as Nylon is a Pita to machine nicely..or they would choose Nylon.
You can crack a 10mm bar of Delrin between both hands, or a casual tap with the hammer if hit sideways in the vice. Try it with Nylon, you will never crack it.

[Ormicron]

Thanks for all the good advice, Nylon, Delrin? The comment on how brittle Delrin is has swayed me. I agree that the Murtfeldt was oiled. It was a greasy plastic very wear resistant its downfall is that it spreads when clamped. I will experiment! Really like the turned up piston head.

[evert]

But isnt nylon infamous for attracting moisture and expanding over time?

[Dave2345678]

But isnt nylon infamous for attracting moisture and expanding over time?

Yes it is but hardly a problem in this application, where 0.1mm to 0.2mm of growth in dia is not going to cause a problem.
Now, if used in place of a Delrin rear piston bearing you might have slight concern where even tiny growth in dia might cause a problem.

[Benelli B76]

Anyway if you feel the need you can precondition nylon before getting finished machining dimensions. Something BSA did not do with piston heads apparently.

Baz