Hmmm.... I think I might have to "long stroke" my TXs....

[Shed tuner]

Got quite used to shooting some of my "softer" shooting guns lately, like the HW80 and the 22mm TX.

The suns's out, so I had a plink with my "regular" 25mm, short stroked TXs.

Hmmm.. Nice and quick for sure, but kinda "aggressive" by comparison. So I lengthened the stroke from 77mm to 81mm (you can't do 79/80, 'cos it catches on the ABT notch on a mk2) on one of them. The difference is subtle, but shooting them side by side, very obvious. The 81 is noticably softer, and a little easier to cock. Doesn't feel any slower (although it almost certainly is), and no obvious change in accuracy. But it's just calmer, more relaxing to shoot.

So maybe 81mm is the magic number for the 25mm guns ? That stroke may be familiar to many of you...

[prosport.177]

I have kinda settled on 84/85mm for my ally piston 25mm. 😊

[TonyL]

The sun was out for you, was it, Jon?

No such luck up here!


Mmmmm.......81mm stroke, eh.....sounds like a 77, no?

Shows that Mr HW knew what he was doing all those years ago, then? I wonder if that figure was arrived at scientifically, or just a stroke (sorry!) of luck?

Jim has done loads of research on this very subject in recent times. And, on some guns, although the firing cycle was declared as "lovely", accuracy and/or hold sensitive did suffer. Just goes to show that the acid test always has to be accuracy and how easily accessed that accuracy is.

As you say, many of the very short stroke guns necessarily exhibit very "fast" actions and higher cocking effort.

Also, taking into account Jim's work, if, say, the all-up gun weight is ten times the weight of the internals involved (piston and a proportion of spring mass) and if the stroke is altered by 10mm, measured recoil will be 1mm. The surge effect will be of more importance.

And some will always be down to personal preference.

Very interesting thread, will be intriguing to see how it develops.

[Shed tuner]

The sun was out for you, was it, Jon?

No such luck up here!


Mmmmm.......81mm stroke, eh.....sounds like a 77, no?

Shows that Mr HW knew what he was doing all those years ago, then? I wonder if that figure was arrived at scientifically, or just a stroke (sorry!) of luck?

Jim has done loads of research on this very subject in recent times. And, on some guns, although the firing cycle was declared as "lovely", accuracy and/or hold sensitive did suffer. Just goes to show that the acid test always has to be accuracy and how easily accessed that accuracy is.

As you say, many of the very short stroke guns necessarily exhibit very "fast" actions and higher cocking effort.

Also, taking into account Jim's work, if, say, the all-up gun weight is ten times the weight of the internals involved (piston and a proportion of spring mass) and if the stroke is altered by 10mm, measured recoil will be 1mm. The surge effect will be of more importance.

And some will always be down to personal preference.

Very interesting thread, will be intriguing to see how it develops.

Yeah, got a tan today - very sunny

As you say 81mm = HW77 stroke, also Mk1 / mk2 TX stroke...

I'm also interested in the hold sensitivity thing, so I'm going to test the two powerplants in the same rifle, one at 77, one at 81, and see if I can detect any hold sensitivity differences. If not, 81mm it is

[NickG]

I do my ally pistons at 77 for competition guns , and 80 for sports, the longer stroke has more sight picture movement.

[Shed tuner]

I do my ally pistons at 77 for competition guns , and 80 for sports, the longer stroke has more sight picture movement.

see it will on yours, cos you have those light pistons, and a std size port. However, when you tighten the port, and up the piston weight to closer to 200g, it balances back out. Would be very interested in the accelerometer data on your guns (not the kitched sideboard stock though - that's cheating ).. my guess is they will be light in recoil, but a fair bit of bounce displacement, and possibly a little slower in terms of pellet exit time, due to the large port volume buffering the compressed air... ironically, almost PCP like

it's interesting eh... you tune for sight picture movement. I tune for speed with a little softness. Some folks tune for "accuracy" but I struggle with that, as they are all really accurate... but one could tune for hold sensitivity... BUT - they are not really opposites. For sure, there are slight compromises that favour one attribute over another, but it's not like adding 3mm stroke for "softness" means the thing jump out of your hands

Next time you come to the bash, trying staying for more than half-an-hour, heh ?

[NickG]

Definitely be there longer next time , circumstances were against me at the last one .

[wonky donky]

I normally tune for 82mm stroke, 198/200gm piston, reduced port lth by 2.7mm.
I like the feel of this tune, very quick with a softer feel, sight picture movement is minimal, no problem seeing pellet strike. 8.46gn & 7.84gn come out at 0.3fpe different.

My test Tx200 is currently running a 160grm piston with 6mm wide rear bearing, 5mm wide front bearing, also fitted on the above, almost making compression at 77mm stroke. standard port
It's harder to cock but not much, again very rapid firing cycle, minimal sight picture disturbance, just as quiet as the above tune but it's very noticeably better with 7.84gn than 8.46gn which feels very bouncy indeed although the difference is as above.

Last saturday I bought a new TX200 from the local shop. I've now fitted it with to above but piston weight at 170gms & stuck with the 77mm stroke & standard port. This tune I don't like, I'm unable to explain why as yet, it's taken 2 more coils on the spring to get the same power as the 160gm piston version but it's not bouncy & both pellets are within 0.1fpe of each other.

I used Walther LGU Seals on all 3 TX's

[Shed tuner]

I normally tune for 82mm stroke, 198/200gm piston, reduced port lth by 2.7mm.
I like the feel of this tune, very quick with a softer feel, sight picture movement is minimal, no problem seeing pellet strike. 8.46gn & 7.84gn come out at 0.3fpe different.

Hi Dave, that's bang on there I'm at now... (well, except for the 1mm diff)... I'm down to even a fraction less difference between the 7.9s and 8.4s - maybe it's due to that last mm

Amazing how things "converge" completely independantly...