I'm an Airgun enthusiast...

The nice thing about polymer seals which form the piston head is that they provide a soft buffer as the piston reaches the end of travel, when BSA used steel O ring piston heads in the 1970s and 1980s they incorporated a polyurethane buffer between piston and head.

I've machined O ring heads from Polyurethane for older air rifles and pistols, for a Weihrauch I'd be inclined to use PTFE and machine it properly to either press fit onto the piston, or use a "Keyhole" slot allowing the head to be installed or removed with the piston out of the bore by sliding it sideways but retaining it securely whilst in a bore where sideways movement is restricted.
Using screws to hold a head on a Weihrauch piston is at best a kludge and lacks engineering imagination and knowledge of air gun history :-(
 
The nice thing about polymer seals which form the piston head is that they provide a soft buffer as the piston reaches the end of travel, when BSA used steel O ring piston heads in the 1970s and 1980s they incorporated a polyurethane buffer between piston and head.

I've machined O ring heads from Polyurethane for older air rifles and pistols, for a Weihrauch I'd be inclined to use PTFE and machine it properly to either press fit onto the piston, or use a "Keyhole" slot allowing the head to be installed or removed with the piston out of the bore by sliding it sideways but retaining it securely whilst in a bore where sideways movement is restricted.
Using screws to hold a head on a Weihrauch piston is at best a kludge and lacks engineering imagination and knowledge of air gun history :-(

I like both of those ideas... if it were press fit would be easiest to attain a secure fit with a slight taper in the bore of the cap. Depending on the material used and the degree of taper this might be no more difficult to install than a tight fitting conventional seal. One gentleman tells me he’s got thousands of shots on a delrin cap and Ed has been using the moly impregnated nylon for some time as well.
 
The nice thing about polymer seals which form the piston head is that they provide a soft buffer as the piston reaches the end of travel, when BSA used steel O ring piston heads in the 1970s and 1980s they incorporated a polyurethane buffer between piston and head.

I've machined O ring heads from Polyurethane for older air rifles and pistols, for a Weihrauch I'd be inclined to use PTFE and machine it properly to either press fit onto the piston, or use a "Keyhole" slot allowing the head to be installed or removed with the piston out of the bore by sliding it sideways but retaining it securely whilst in a bore where sideways movement is restricted.
Using screws to hold a head on a Weihrauch piston is at best a kludge and lacks engineering imagination and knowledge of air gun history :-(
I've corresponded with Ed and others a fair amount on this piston cap and had forgotten the exact reason for the set grub screws mounting the cap. If you measure the seal retaining button on an HW piston apparently a fair number are not perfectly centered on the piston and given the closer tolerances needed in order to seal an OPC, the solution has been to mount the piston cap and then turn the final dimensions in place on the piston. I'm sure a clever person could overcome this in another way, perhaps chucking the piston and turning the button to a smaller diameter and then making the cap. Of course then a standard seal could never be used on that piston but I wouldn't think that's an issue. At any rate, that is how we got to where we are.
 
I'm sure a clever person could overcome this in another way.

There are many pre-existing solutions for retaining heads on pistons I was just a bit surprised by the screws, making the head over-size on the OD and making it a tight snap-fit when pressed on would still allow machining the OD to size on the piston, just without the screws ;-)

If seeking ultimate repeatability I'd also button the piston at the rear-most point that doesn't protrude from the cylinder when cocked, otherwise it's almost certain to have metal to metal contact with the bore at some point.
Also a sleeve for the spring inside the piston (join at 180 degrees to the slot) will minimise lubricant migration, plus internal spring guides supporting the full length of the spring in it's cocked state reduce losses due to unwanted distortion of the spring.
 
There are many pre-existing solutions for retaining heads on pistons I was just a bit surprised by the screws, making the head over-size on the OD and making it a tight snap-fit when pressed on would still allow machining the OD to size on the piston, just without the screws ;-)

If seeking ultimate repeatability I'd also button the piston at the rear-most point that doesn't protrude from the cylinder when cocked, otherwise it's almost certain to have metal to metal contact with the bore at some point.
Also a sleeve for the spring inside the piston (join at 180 degrees to the slot) will minimise lubricant migration, plus internal spring guides supporting the full length of the spring in it's cocked state reduce losses due to unwanted distortion of the spring.
Both of my 97's are set up just so. Except for the buttons on the rear of the piston. Ed's pistons typically have a delrin ring let into the rear of the piston.
 
I'm kinda surprised that nobody wants to give this a shot. I'm interested enough to buy my own lathe and do it myself but I just spent $4000.00 on irrigation design software so I'm tapped out on discretionary spending.
 
I really don’t know what an hourly rate should be or how long such a job should take. I was hopeful that the enthusiasts here could tell me. FWIW I believe NCED was building an oRing cap for 75.00 or so. But I cannot tell if that’s fair or not?
 
I really don’t know what an hourly rate should be or how long such a job should take. I was hopeful that the enthusiasts here could tell me. FWIW I believe NCED was building an oRing cap for 75.00 or so. But I cannot tell if that’s fair or not?

That sounds like a fair commercial price, if you were in the UK I'd probably be able to do you something which worked out better but international postage would kill it :-(
 
Yes, airgunning in the old world is much different than here more and more inventive tuners I would say.. c’est la vie!
 
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