I'm really starting to think that these 21/22mm bores with their longer strokes...

[ART1969]

At the very first Boinger Bash, Wonky Donky brought along a short stroke '80. I seem to recall that the stroke was 55mm and I also seem to think it had a lightened piston; don't think it was running piston bearings.

It shot beautifully!

Barely distinguishable from a 25mm sleeved one.. ----- Obviously just going on perceived feel here, it would need a rig such as discussed above to measure for sure.

So, assuming for a second that it yielded similar results, the short stroke and standard bore would entail far less work.

But we love it when these shed tuner techies play around!

He took a 55mm stroke 77 to Kinver ARC some time back. You could barely tell it had gone off.

[Snooper601]

He took a 55mm stroke 77 to Kinver ARC some time back. You could barely tell it had gone off.

I'm not surprised, at 55mm stroke a 77 would only make about 6fpe because of the lack of swept volume.

Cheers

John

[TonyL]

I'm not surprised, at 55mm stroke a 77 would only make about 6fpe because of the lack of swept volume.

Cheers

John

HW80, John.

[Snooper601]

HW80, John.

Probably, but that's not what was written, he wrote 77.

Cheers

John

[wonky donky]

At the very first Boinger Bash, Wonky Donky brought along a short stroke '80. I seem to recall that the stroke was 55mm and I also seem to think it had a lightened piston; don't think it was running piston bearings.

It shot beautifully!

Barely distinguishable from a 25mm sleeved one.. ----- Obviously just going on perceived feel here, it would need a rig such as discussed above to measure for sure.

So, assuming for a second that it yielded similar results, the short stroke and standard bore would entail far less work.

But we love it when these shed tuner techies play around!

The 80 you shot Tony was 65mm stroke, piston lightened by turning the whole body down a little & machining two full length slots 13mm wide equall distence from the cocking slot. button bearings fitted nose & tail. T.port was 3.6mm. I did do a 55mm stroke version which was nowhere near as good.

He took a 55mm stroke 77 to Kinver ARC some time back. You could barely tell it had gone off.

I'm not surprised, at 55mm stroke a 77 would only make about 6fpe because of the lack of swept volume.

Cheers

John

The 77 was a 25mm version in .22 with a 68mm stroke lightened piston with bearings & 3,9mm T.port. Both the 80 & 77 made UK power limits easily but there was a wide variation from pellet to pellet. RWS Superdome gave the highest test Vo in both, this was a complete reversal from when the rifles were standard.

I've always said you can tune a rifle for one of the high quality makes of pellet available at the expense of other makes......the question is, should you? Accuracy IS the most important thing at the end of the day, by tuning just for one brand & weight range your limiting choice, but that's another story.

hope this helps

[Snooper601]

The 80 you shot Tony was 65mm stroke, piston lightened by turning the whole body down a little & machining two full length slots 13mm wide equall distence from the cocking slot. button bearings fitted nose & tail. T.port was 3.6mm. I did do a 55mm stroke version which was nowhere near as good.





The 77 was a 25mm version in .22 with a 68mm stroke lightened piston with bearings & 3,9mm T.port. Both the 80 & 77 made UK power limits easily but there was a wide variation from pellet to pellet. RWS Superdome gave the highest test Vo in both, this was a complete reversal from when the rifles were standard.

I've always said you can tune a rifle for one of the high quality makes of pellet available at the expense of other makes......the question is, should you? Accuracy IS the most important thing at the end of the day, by tuning just for one brand & weight range your limiting choice, but that's another story.

hope this helps

Hi Dave, that makes much more sense, the variation ties in with Jim's latest article regarding thickness of pellet skirts and the starting pressure of the pellet 's first movement up the barrel.
He concludes that the stiffer walled pellets start at a much higher pressure and therefore are more prone to dieseling.

Falcon accuracy plus versus RWS Hobby gives a good guide to sè if dieseling is occurring, if the Hobbies produce more power than the FAP then it's probably dieseling with tight stiff pellets, particularly in short stroke or reduced swept volume cylinders.

Cheers

John

[T 20]

Hi Dave, that makes much more sense, the variation ties in with Jim's latest article regarding thickness of pellet skirts and the starting pressure of the pellet 's first movement up the barrel.
He concludes that the stiffer walled pellets start at a much higher pressure and therefore are more prone to dieseling.

Falcon accuracy plus versus RWS Hobby gives a good guide to sè if dieseling is occurring, if the Hobbies produce more power than the FAP then it's probably dieseling with tight stiff pellets, particularly in short stroke or reduced swept volume cylinders.

Cheers

John

Hi John

Jim's latest article explains a lot about these small swept volume guns, my own HW35 with LGV piston gives some weird velocity figures --- it runs at 800fps using Superdomes yet only runs at 700fps with equal weight pellets from other manufacturers.

It also runs very consistently at the lower power level with Hobbies.

This problem didn't show when I had a .22" barrel fitted and is probably due to the lower cylinder pressures required.

All in all another bloody good article from Jim which I'll need to read again to get the full benefit from.





All the best Mick

[Snooper601]

Hi John

Jim's latest article explains a lot about these small swept volume guns, my own HW35 with LGV piston gives some weird velocity figures --- it runs at 800fps using Superdomes yet only runs at 700fps with equal weight pellets from other manufacturers.

It also runs very consistently at the lower power level with Hobbies.

This problem didn't show when I had a .22" barrel fitted and is probably due to the lower cylinder pressures required.

All in all another bloody good article from Jim which I'll need to read again to get the full benefit from.





All the best Mick

Yes Mick, it echos what we were discussing at the last bash.
I'd still like to pin down the exact reason for the o-ring versions dieseling more than the parachute seal versions.

Jim needs some TX short stroke adapters, all producing the same stroke, so that he could compare o-ring, TX and HW style seals in the same gun.
If i had my lathe running I'd make him a set and also test my TX with the same ones.

Cheers

John

[ART1969]

Probably, but that's not what was written, he wrote 77.

Cheers

John

It had an underleaver though maybe I misheard the stroke

[T 20]

Yes Mick, it echos what we were discussing at the last bash.
I'd still like to pin down the exact reason for the o-ring versions dieseling more than the parachute seal versions.

Cheers

John

It could all be down to piston breaking John

Cardew showed the increase in cylinder pressure to have very little effect on the friction created by an O ring seal but did increase the friction created by a parachute seal.

So maybe it's down to the faster temperature rise due to piston speed ?




All the best Mick

[TonyL]

Probably, but that's not what was written, he wrote 77.

Cheers

John

Oops, sorry, my mistake.

[TonyL]

The 80 you shot Tony was 65mm stroke, piston lightened by turning the whole body down a little & machining two full length slots 13mm wide equall distence from the cocking slot. button bearings fitted nose & tail. T.port was 3.6mm. I did do a 55mm stroke version which was nowhere near as good.





The 77 was a 25mm version in .22 with a 68mm stroke lightened piston with bearings & 3,9mm T.port. Both the 80 & 77 made UK power limits easily but there was a wide variation from pellet to pellet. RWS Superdome gave the highest test Vo in both, this was a complete reversal from when the rifles were standard.

I've always said you can tune a rifle for one of the high quality makes of pellet available at the expense of other makes......the question is, should you? Accuracy IS the most important thing at the end of the day, by tuning just for one brand & weight range your limiting choice, but that's another story.

hope this helps

Thank you for the clarification, Dave, and hope you're keeping well.

[TonyL]

It could all be down to piston breaking John

Cardew showed the increase in cylinder pressure to have very little effect on the friction created by an O ring seal but did increase the friction created by a parachute seal.

So maybe it's down to the faster temperature rise due to piston speed ?


All the best Mick

Could well be, young Mick.

These two latest articles by our treasured Jim are very thought provoking and enlightening. As you say, must read again.

In very simple, sort of non-techie terms (and, obviously our humble springers are much more simple in component number terms than engines), and as we and many have said before, it's maybe a bit like tuning a smaller engine to make the same power as a larger capacity one. It can be done, but it's running more "highly stressed" though not in terms of, say, possible breakages, but things start to get maybe more critical, as a smaller engine would be peaky. Compressing that smaller volume has to be done "harder" creating more temperature.

Maybe Jim's reference to the sectional density of the piston could be the key to reducing piston bounce on Jon's example, as it shoots softly whilst making power, but with so very little spring?

[MattyBoy]

At the very first Boinger Bash, Wonky Donky brought along a short stroke '80. I seem to recall that the stroke was 55mm and I also seem to think it had a lightened piston; don't think it was running piston bearings.

It shot beautifully!

Barely distinguishable from a 25mm sleeved one.. ----- Obviously just going on perceived feel here, it would need a rig such as discussed above to measure for sure.

So, assuming for a second that it yielded similar results, the short stroke and standard bore would entail far less work.

But we love it when these shed tuner techies play around!

You may have shot my 50mm HW80 at the June bash Tony? It's running a rear bearing and a 30mm double o-ring piston nose - Bigtoe ran it up as a test/project then swapped it out with me for a std one. It's running a little Titan number 5 with low preload.

It's now rebarreled at 11 Inches in .22 rather than the original full length .22 and it balances lovely and I think the cycle is good.

I have not messed with the piston weight yet allthouth the rear skirt was obviously removed for the full length inner sleeve with integral rear bearing.

Matty

[TonyL]

Can't remember having a go with that one, Matty, although that's no guarantee that I didn't, as there are always SO many nice guns there to try and so many people to talk to that, sometimes, some Bash elements go a little blurry.

Now, I know you said you couldn't make the one next weekend, but now I think you'll have to make further plans, come along, bring the '80 and jog my memory.

Hope you're keeping well, my friend.