sleeving versus stroking....

[Shed tuner]

It could be even better if the piston was lighter weight..however with that comes increased cocking effort...i will see what its like here for an extended period first i think.

The LGU is up next for surgery..all depends on sleeve tube. The piston will just be reduced in dia, nose machined back and an alu nose screwed on with O ring...same spec as the 77. Only difference will be LGU has 3.5mm TP...will see if that helps or hinders.

All good For sure cocking effort vs more spring/lower piston weight is the trade off - kinda like driving a nail in - you can use a light hammer and hit with with all your might, or a heavy one and give it a moderate tap... Trouble is with airguns whilst there's no doubt the heavy piston is efficient at compressing air, moving an unnecessarily large hunk of metal around has some downsides. Nail bashing is simpler.

BTW Your peak pressure comment earlier - I think you are right, what I meant was that for a given pressure, the actual force decelerating the piston would obviously be less, as the surface area upon which it's acting would be reduced. I think that's what would enable a higher peak pressure to be achieved (as the piston would decelerate more slowly as the pressure built up).

Gotta try and do my 23mm TX conv this weekend... it's my birthday, so I may elect to celebrate by sodding off to the shed for the day

[NickG]

You have got me itching to give the 23mm a go, I have a tx comp tube, and I have a 97 comp tube , and I have hydraulic tubing that would lend itself to the job, trouble is my 77 stock is back at custom stocks being rectified, and the tx is the test bed for my buttoned ally piston, that's a dilemma

[NickG]

My Dilemma has just got worse, my neighbour has just handed me my 77 stock, the gun is my 25mm rotating piston, and I want to bring it to the bash. May have to do the tx in 23mm

[bigtoe01]

Did 20 mins testing during lunch break, bismags and jsb heavies noticeable difference in shot cycle, more thump in the shoulder, power was 10.8 to 11fpe however.

FTT's and Exacts utterly beautiful. 8gr Prems were nice also....(shot cycle same with all)

If I can find a few falcons I will see what its like with the light weights....right now though it feels so good with the mid weights im not to worried.

Im kicking myself i did hardly any testing with the previous piston i made, although it worked ok I seem to remember using a spring with way more cocking effort which put me off a little.

I just can't get over how much power it made with the spring from the 26mm set up...13+, the new spring is thinner wire and near 20mm shorter! Its only running 19mm total preload, its easier than a TX to strip now LOL

[greenwayjames]

Small bore compression tubes are definitely worth spending time on. I have a lasting fond memory of being allowed to use an experimental springer made by JB in the 1980s that featured a 7/8" (22mm) diameter piston. It was fingertip easy to cock and with virtually no movement on firing. He told me it was him that steered Gamo away from the bigbore 1250 cylinder bore to a small bore for the high power US market.

[bigtoe01]

Small bore compression tubes are definitely worth spending time on. I have a lasting fond memory of being allowed to use an experimental springer made by JB in the 1980s that featured a 7/8" (22mm) diameter piston. It was fingertip easy to cock and with virtually no movement on firing. He told me it was him that steered Gamo away from the bigbore 1250 cylinder bore to a small bore for the high power US market.

Yeah i heard the same story from another source. One direction we are going different to Bowkett is piston weight, he favours heavy pistons, where we are going light weight.

[vobster]

I found some 1" 18 swg seamless stainless on t'internet, so have that coming along with some aluminium same size for the sleave in the 97 comp tube. I suspect the aluminium one wont get used and I'll just dive in with the SS.
I 'think' I can get the piston sorted by either getting one reduced in a lathe, or make a new body from an aluminium tube, fitted to a bodyless 97 piston I have kicking about.

It will be 81 or 82mm stroke, and I'd like 10ftlb or so. I am thinking of starting with 170-200 grams on the piston and 3.7mm on the transfer port (because the comp tube I have free is 3.7mm )

Does any of that sound wrong?

[greenwayjames]

Yeah i heard the same story from another source. One direction we are going different to Bowkett is piston weight, he favours heavy pistons, where we are going light weight.

He didnt mention piston weight but my guess is reduction of it was probably one of the reasons for experimenting with small diameter pistons. It doesnt make sense to suggest he would automatically use heavy pistons because he "favours" them. Whatever he used it certainly worked.

[NickG]

I found some 1" 18 swg seamless stainless on t'internet, so have that coming along with some aluminium same size for the sleave in the 97 comp tube. I suspect the aluminium one wont get used and I'll just dive in with the SS.
I 'think' I can get the piston sorted by either getting one reduced in a lathe, or make a new body from an aluminium tube, fitted to a bodyless 97 piston I have kicking about.

It will be 81 or 82mm stroke, and I'd like 10ftlb or so. I am thinking of starting with 170-200 grams on the piston and 3.7mm on the transfer port (because the comp tube I have free is 3.7mm )

Does any of that sound wrong?

My plan is 80mm and 170 gram piston, and see what happens

[Shed tuner]

My plan is 80mm and 170 gram piston, and see what happens

Yeah, I'm starting around there; can always shorten the rod / increase the stroke if needed...

[bigtoe01]

He didnt mention piston weight but my guess is reduction of it was probably one of the reasons for experimenting with small diameter pistons. It doesnt make sense to suggest he would automatically use heavy pistons because he "favours" them. Whatever he used it certainly worked.

going by his tune on the 77 he documented in AGW and the gun we all shot he tuned at the boinger bash I came to the conclusion he would use a heavier piston...

Either way, 23mm works, 7/8th is 22.7 so near enough the same.

[greenwayjames]

going by his tune on the 77 he documented in AGW and the gun we all shot he tuned at the boinger bash I came to the conclusion he would use a heavier piston...

Either way, 23mm works, 7/8th is 22.7 so near enough the same.

JB hasnt done any spring airgun conversion for at least twenty years so unless he recently serviced the 77 you shot at the Boinger Bash it isnt really representative of his work. His conversions were not DIY servicable even by experienced bodgers. Having said that, how can conclusions on what was inside a one off experimental air rifle that you have never seen or used be drawn by shooting a HW?
Either way 7/8" worked in the rifle I was allowed to shoot so we can agree on that

[bigtoe01]

JB hasnt done any spring airgun conversion for at least twenty years so unless he recently serviced the 77 you shot at the Boinger Bash it isnt really representative of his work. His conversions were not DIY servicable even by experienced bodgers. Having said that, how can conclusions on what was inside a one off experimental air rifle that you have never seen or used be drawn by shooting a HW?
Either way 7/8" worked in the rifle I was allowed to shoot so we can agree on that

you talk like you are Bowkett...are you?

either you are him or you are a stalker...which is it?

[greenwayjames]

you talk like you are Bowkett...are you?

either you are him or you are a stalker...which is it?

No but I've had a Stalker - it was an FAC Leopard. Very nice. 920fps .22" Bis Mags. The bunnies celebrated the day I moved it on to make room for another goodie on my ticket

BTW do you know JB? You seem pretty sure of what he did and didnt do. I assume you are a drinking buddy of his?

[Shed tuner]

JB hasnt done any spring airgun conversion for at least twenty years so unless he recently serviced the 77 you shot at the Boinger Bash it isnt really representative of his work. His conversions were not DIY servicable even by experienced bodgers. Having said that, how can conclusions on what was inside a one off experimental air rifle that you have never seen or used be drawn by shooting a HW?
Either way 7/8" worked in the rifle I was allowed to shoot so we can agree on that

JBs work on springers is well documented to generally include adding a lump of weight to the piston.
Now I'm not saying that's "bad" per se, in as much as it will often help efficiency. However it can also somewhat increase recoil. But the real potential downside is that the shot cycle isn't so nice, feeling slammy. This almost certainly won't have any affect on accuracy, as per the other thread you started and we answered about when the pellet leave the barrel in the cycle, but it does mean the second fwd stroke of the piston crashes somewhat unpleasantly. It may even enhance accuracy, as the piston will decelerate more slowing at the end of the first fwd stroke before bounce back.

Ref the example above, 30 years may have passed, but I doubt the weight of the piston or the size of the transfer port has magically changed by itself in that time

I'd also say that the guy did some great work on springer tuning, but the "addi ng weight to the piston" direction was a bit simplistic IMHO.

I'd also read of his 7/8" cylinder gun - wonder why it never made it to "production" ? Can you ask him next time you call him?