sleeving versus stroking....

[vobster]

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?

Strange that your name is also john.

[greenwayjames]

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?

I will.

[POK!]

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?

Sometimes BBS'ers like to think they're inventive and pioneering. Point out it's been done before, often decades ago and they'll try and rationalize things so their ideas are still novel. There's always room for improvement but the implication "Bowkett was wrong" is unnecessary but fairly typical unfortunately.

[vobster]

What a shame JB didnt get his 7/8 into production, set springers back twenty years!

But then he was always in it for the money, where as the open knowledge of the bbs tuners is to the benefit of all. Because information was not shared, it needs to be rediscovered.
Of course, the benefit of the rediscovery is that its done in the open without an agenda, and we can share and learn from each other, giving a better result in the end.

[NickG]

What a shame JB didnt get his 7/8 into production, set springers back twenty years!

But then he was always in it for the money, where as the open knowledge of the bbs tuners is to the benefit of all. Because information was not shared, it needs to be rediscovered.
Of course, the benefit of the rediscovery is that its done in the open without an agenda, and we can share and learn from each other, giving a better result in the end.

Research and development is faster and more effective when done by individuals, and then shared, the more people that are involved the better it gets, and there are no constraints so who knows where it will go, exciting. imo

[TonyL]

Just a quick thought, chaps, to see how relevant this may be.....

Once correctly set-up, I think it was mentioned above that the narrow bore gun would be less impeded by friction.

But, also, with the narrow bore / longer stroke, would this set-up produce higher cylinder temperatures, which would also aid efficiency, providing the air with more energy?

[BTDT]

Just a quick thought, chaps, to see how relevant this may be.....

Once correctly set-up, I think it was mentioned above that the narrow bore gun would be less impeded by friction.

But, also, with the narrow bore / longer stroke, would this set-up produce higher cylinder temperatures, which would also aid efficiency, providing the air with more energy?

The retarding force from the compressed air on the piston at any point in the compression stroke is a function of the piston's cross sectional area. Provided that the piston sectional density and the spring energy are maintained, a narrower piston will travel a fraction further, and achieve higher cylinder pressure and temperature.

The beauty of having a narrower piston is that it can maintain the sectional density of a wider one while having less mass, which means less recoil displacement. IMO this is a very promising area of springer research.

[greenwayjames]

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?

I put your question to him in a phone call earlier this morning.
He said that it was first made about 1982 as an experimental jig in a search of knowledge about the effects of using different diameter pistons and stroke lengths. It was never intended for production. It was in fact a 1" diameter piston model that could be reduced to 3/4" via 7/8" could also use different stroke lengths. The version I tried was in 7/8" diameter and was perfect for 12 ft/lbs use. At the same time he went to the other end of the scale and made another rifle to find out the results from a very large (1 5/8" diameter) piston using an extremely short stroke.
At the end of the 1980s he made a unique spring air rifle for Titan using many parts from the Manitou, Mohawk. This again never went into production as he left Titan but used a very small frontal area piston but in a diffent way to the earlier one. Normal size air rifle springs could be used. It was an unusual layout with the spring at the muzzle end with a piston having the sear rod passing through the compression cylinder end wall to engage a trigger closest to the butt. The compression cylinder was sandwiched between the spring and trigger unit
This information was shared with other airgunners via an article in Airgun World and more recently details of it was put up on the Facebook Fanpage for John Bowkett

I hope this answers your query

[bigtoe01]

The retarding force from the compressed air on the piston at any point in the compression stroke is a function of the piston's cross sectional area. Provided that the piston sectional density and the spring energy are maintained, a narrower piston will travel a fraction further, and achieve higher cylinder pressure and temperature.

The beauty of having a narrower piston is that it can maintain the sectional density of a wider one while having less mass, which means less recoil displacement. IMO this is a very promising area of springer research.

Jim

Im sorry you won't be reading what I am up to regarding springer tuning any more on the BBS, im not leaving, i just feel my input would be better on other forums and FB so no more technical posts from me here.

Im not going to read what mr I live in saxmundham but my IP is from the Birmingham area has to say...he is on ignore again and will stay that way.

[TonyL]

Jim

Im sorry you won't be reading what I am up to regarding springer tuning any more on the BBS, im not leaving, i just feel my input would be better on other forums and FB so no more technical posts from me here.

.

........Which would be a huge loss and massive shame for all here.

I know that I won't be alone in saying this but Tony, Mick, Jon, Nick , Wonky Donky and many, many others offer an invaluable technical insight into springer tuning. Not just on tuning, but also freely dispense tips and information on repairs etc.

Now, I don't have the time, space or equipment to be able to perform some of the re-engineering jobs that the aforementioned seem to be able to do in their sleep. I have done spit and polish tunes and more simple jobs for years. I've been into springers for a long, long time and feel I have a pretty good understanding of many of the concepts and theories. If I had the equipment and time and then also the spare money (to buy project rifles) I'd be at it. But, sometimes, I feel that I wouldn't have the confidence or bottle to undertake some of the jobs these guys can do, for fear of spoiling a previously good gun.

Their input is invaluable, either for others wishing to try similar modifications, or simply to log in their "springer knowledge bank" and I feel indebted that they are willing to freely share their knowledge and findings.

So, we have the professional tuners doing their thing, we have the excellent Technical Airgun Series from Jim and we have the BBS "shed tuners". Long may this continue.......

[greenwayjames]

ive noticed of late 2 trends .. firstly the ever de-creasing bore size [sleeving down to 23mm now from nick]
and ive also spotted daves work from stroking a [i think] 30mm chamber to something around 45mm
and that got me wondering which is best ?
my innitial thoughts are thus........
a narrow bore and medium stroke should give better flow to [and through] the transfer port....... all the pressure and turbulence is directed from a much narrower band toward the port, this maybe great for efficiency ? !

but....... on the other hand, a 40 something mm stroke [despite having a larger bore] should give a rediculously fast lock time...... reducing hold sensitivity hugely ?
so i guess the question is, which direction is favourable in terms of muzzle flip/recoil reduction ?

As I was saying before the interruption - the 7/8" bore experimental rifle that I shot was a total joy. Definitely the right way to go for UK limits so why bother making another rifle with an enormous bore, I asked. The answer was to make the powerplant more compact especially if a piston wall trigger system was used rather than a piston rod with trigger mechanism in line. The other area JB wanted to look at was that of power for export markets where, if the cost could be in the right ballpark, the largest market for the product lay. I will ask if the bigbore powerplant is still about and if I can have a try. I will report the results if allowed. BTW JB said he still had a considerable quantity of 7/8" bore x 1/16 wall good quality seamless tubing if anyone wanted to have a go at sleeving but only required a short length. If only a few inches, for a sleeve, were needed he only wanted postage costs.

[Shed tuner]

BTW JB said he still had a considerable quantity of 7/8" bore x 1/16 wall good quality seamless tubing if anyone wanted to have a go at sleeving but only required a short length. If only a few inches, for a sleeve, were needed he only wanted postage costs.

I'd like a couple of short lengths please... around 4.5" long should be enough - all I've found so far is 23mm ID 26mm OD, which is a bit tedious to turn down (just spent 30 mins doing it in fact !) please PM us your details for payment / postage / £££ etc ta - JB

Also tks for the other info, pity it never "made it"...

(goes back to the garage to finish off his own 23mm experiment; tube done, piston done, just the o-ring nose to finish and the comp tube trans port do do now - maybe today I should have something )

[greenwayjames]

I'd like a couple of short lengths please... around 4.5" long should be enough - all I've found so far is 23mm ID 26mm OD, which is a bit tedious to turn down (just spent 30 mins doing it in fact !) please PM us your details for payment / postage / £££ etc ta - JB

Also tks for the other info, pity it never "made it"...

(goes back to the garage to finish off his own 23mm experiment; tube done, piston done, just the o-ring nose to finish and the comp tube trans port do do now - maybe today I should have something )

You woud have to contact JB direct and ask him for the tubing. 0121 745 4287. I dont wish to get involved but just extended his offer to any bodgers here

[NickG]

Bodgers,? That's a bit derogatory, are you some sort of expert then, I assume you have engineering credentials ?

[greenwayjames]

Bodgers,? That's a bit derogatory, are you some sort of expert then, I assume you have engineering credentials ?

After bodgers i used the . Dont be so grumpy.

And no I dont have any credentials, especially in the cold weather