I'm an Airgun enthusiast...

Hi Steve,

I could maybe help you out with this however I am based in the UK so shipping could be a pain. That being said if you’re struggling to find someone to do it for you then it may well be worth the trouble.

It looks easy enough to do although I know very little about air guns and even less about modifying them so anything I do will be based purely on your instruction.

If you’re interested drop me a PM. I’d like to know the following before fully committing to anything:
  • What material would it be made from? I think a few suggestions have been thrown out there in this thread although your original post stated Derlin. If I were to order some I’d end up having to order far more than I would actually need. Alternatively if you’d be happy with brass/aluminium/nylon then I would probably have something in the scrap box.
  • What size of O ring would be going in there?
  • Is there a ± tolerance on the diameter? My concern would be that the piston does not look like a machined part and will therefore most likely be out of round. If I machine to the exact size as the tool runs off the end of the piston the cut will more than likely run onto the piston itself. I suppose that this may not be an issue so this is more to make you aware. I suspect that the part is machined slightly oversized to allow for this. The other option as you mentioned earlier is that I could machine the seal head down and then bore the new piece to suit. The downside to this would be that you can’t then revert to original so if it’s an expensive part to replace it’s probably better to accept that the first few mm of the piston may have some machining marks on it.
  • The drawing states about 0.4” thick. Is this dimension critical or is it machined to fit? i.e. will I need to test fit to determine this dimension?
It would probably take me a few weeks to do. As I said before it’s not a big job although I’ve dozens of small jobs lying around the workshop which collectively take up most of my free time!

Thanks,

Sam
 
It might be easier to have a new compression tube and piston shipped to you in the UK and have you do that work there. Parts for this model are not easily available, or as inexpensive as they are over there. Parts number P105 and P085 are the compression tube and piston respectively. You'll need both in hand to do this work. The guys who've done this over here tell me that since the tolerances for O-ring sealing are very close, you need to check the tube to be certain that it's the correct diameter and consistent with that diameter over the length of the tube.
The cap can be made from whatever you have handy. If nylon, it would need to be heat resistant to some degree, we're compressing air over 300 to 1 ratio and that generates some heat.
The piston is undersized compared to the tube by at least one mm and you're right, the button which retains the stock seal is usually not exactly centered so guys who've done this successfully will mount the cap and then turn the piston/cap assembly as one piece.
I'm not sure what O-ring would be needed.

Airgun-Diagram3 77 AND 97K.gif
 
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