Piston orings

[TonyL]

Maybe possible to mitigate a little with less piston mass and less spring force, as long as power is acceptable? Or maybe go for slightly more crush with a wider section 'O' ring?

[NickG]

Maybe possible to mitigate a little with less piston mass and less spring force, as long as power is acceptable? Or maybe go for slightly more crush with a wider section 'O' ring?

I believe bits the lack of braking as mentioned by john

[32:1]

Maybe possible to mitigate a little with less piston mass and less spring force, as long as power is acceptable? Or maybe go for slightly more crush with a wider section 'O' ring?

Pistons are lightweight as they come, I’ll get back into it later this week. If I can get a consistent fps I’ll then know if I can lessen spring and I’m thinking of a double oring nose to see what that does.

[TonyL]

I believe bits the lack of braking as mentioned by john

Couldn't disagree with your vast knowledge and experience, Nick.

[Shed tuner]

Couldn't disagree with your vast knowledge and experience, Nick.

yeah, don't listen to me

[TonyL]

yeah, don't listen to me

You know I always do, Jon.

[Shed tuner]

You know I always do, Jon.

[32:1]

I’ve spent far to much time on this oring head and still can’t get a consistent fps

Going back now and will test a few parachutes now, 26mm bore so a HW, Norica and the new Cometa seal

Let’s hope we get a result 😂😂😂

[TonyL]

Again, those fine gentlemen Shed Tuner, NickG and T20 are the best qualified to advise accurately, but from my understanding and experience, the 'O' ring needs an amenable cylinder environment to perform at its best. Poor cylinders would be very unforgiving. After that, you need the groove depth / crush to be correct and ensure that you lubricate very sparingly. Correctly set-up 'O' rings can deliver extremely consistent performance. But the parachute seal has proven itself to be very forgiving, reliable and durable.

[32:1]

I thought I’d just install an Oring nose and that would be that, how wrong 😂😂😂

There’s something in this modifying lark 😉

I’ve deburred it, cleaned the bore and it looks good to me, tried near 10 noses with three different oring sizes, some have pressured when pushing down some are just slower, firing can be 150fps different ranges and then the best I’ve managed is 25fps spreads and they all feel harsh to shoot, nothing cushioned about any of them, it might be the cylinder or Tp or the small volume of the gun

Dropping the original piston and seal back in delivers that cushioned feel and that I’m sure is the seal hitting home rather than the delrin or aluminium oring nose(s). The original piston has its own issue with the dovetail being a wee bit to small and the seal can flex/move, does anyone know of a DT fitting seal that has a solid front so it only the outer edge to seal pressure


This has a 26mm bore

Chris

[TonyL]

Most of the seals I've come across seem to move a little bit on the dovetail and, to be fair, my guess would be that performance or efficiency would be unaffected. Possibly worrying a little too much over something that isn't an issue? If it did continue to concern, you could try to pack the dovetail out slightly? Or maybe some sort of mastic type medium, soft-grip glue, soft thread lock, tape or something? I've always noted a slight movement on the seal fit, but never been tempted to address it. Could it even be counter-productive?

[TonyL]

Re the harshness, I'm sure it'd just be a case of balancing things out with seal fit & friction (size and crush and groove depth), TP, piston weight, spring force etc. Pretty much as you'd do with any system if fine tuning? And maybe BSA knew plenty back in the days when they used the 'O' rings, with their buffer system? Shame they ended up using a material that degraded and swelled, though. I see the Protek buffers are said to be much better, making the best of modern materials?

[Shed tuner]

you might be over-sprung.. they require less spring, and defo less preload too

[xbow]

I’ve only ever used O rings in static applications so I did a google, as you do.

Are folks on here using these types or something else?

[32:1]

Had a little bit of progress today 😎

I fitted a 2mm oring and cut 1mm groove and was planning to modify from there but no need as we had decent fps and far better consistency than before, still feels harsh to me but some might call it fast.

I ran a test with the same piston and original spring and guide and simply fitted four different seals via a m6 thread, a few shots to settle down and then ten through chrono and took average of the same 8.44 JSB.

Hw 638
Oring 666
Cometa 650
TWChambers 680


This .177 220 has near 50mm of preload and my .22 has 15mm, the triggers are basic and this .177 is firmer and I’m guessing it’s the extra spring tension so I may drop fps down a little and see if it improves break