AirGunTech: Re Engineering Spring Powered Air Rifles for smoothness, consistency, and to better suit UK power levels.

Could this be the ultimate piston seal?

Been looking for an alternative seal now for a while, something off the shelf, easy to find and that works as well as an O ring if possible with minimal lost volume. Scouring the Hydraulic seal suppliers I came across Kastas.

Click the pic for a link to the site, I highlighted the seal I will be testing next on 25mm pistons.

Kastas seal


The reason for this seal was its size, it is around the same size as an O ring but is made of polyurethane, the pressure groove is tiny so the lost volume should be minimal and the seal sits in an easy to machine flat bottomed groove. My plan is to test the seal with flat fronted pistons (bronze piston nose) running tight tolerances to minimise the lost volume even further.

Some addition pics of the seal.

















Will update with some results and installation pics as the seal, as you can see its pretty small.


  • Whilst researching polyeurethane machining i came across these people . maby if you draw the perfect seal they could manufacture it

  • The general plan is to find an off the shelf one to keep the costs down I could machine my own although PU can be a pig to machine.

    I already tested a slightly larger version of this seal (wider) and the results were very encouraging, hence i search out this thinner model to try.

  • Tony, that could well be an end to lost volume around piston noses, maybe you could trial one on the boys 30 piston?

  • Excuse my ignorance in this matter but how much of an effect does lost volume really play when tuning springers, can it really make a lot of difference in the overall performance of the rifle?

  • Hi Tony, curious to see how this is working out so far. I was going to send my pistons off to be O-ringed but I’d rather wait and see the outcome here.

  • Been looking at a similar site. Checked out your supplier though and they have a two part seal I was going to test in my o ringed piston comprising of an o ring with a PTFE ring which sits on top of it in the same groove.

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