sleeving versus stroking....

[slugger]

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 ?

[Shed tuner]

Long and thin should be more efficient, also less pressure to cause (inevitable) piston bounce, hence a lighter piston can be used, which moves faster, less recoil etc. I've high hopes of 23mm

[slugger]

ok, so what about going to extremes ?
take for example my 48....... i think it has a stroke length of around 110 mm... could you in theory keep the stroke, but sleeve id down to say 20mm ? assuming of course you could find a narrow enough spring

[bigtoe01]

ok, so what about going to extremes ?
take for example my 48....... i think it has a stroke length of around 110 mm... could you in theory keep the stroke, but sleeve id down to say 20mm ? assuming of course you could find a narrow enough spring

optimum stroke is around 80mm give or take up and down a little, larger gives a lazy shot cycle, shorter can feel thumpy.
so...your 48 needs a sleeve to 25mm and a nice old LGV piston in it with a nice longer piston rod to set to around 75mm stoke...so the feel is right. The power comes easy...to easy so thats not an issue.

Its about the shot cycle, not the amount of air, i think you are getting fixated with the volume of air being compressed...i went this way first, then realised there is a reason the 77 was set to 81mm and the mk1TX to 83mm...yes you can go shorter to say 77mm but you have to remain close to the ball park to get the right feel.

[TonyL]

I do not have the time, equipment or skills to perform the re-engineering jobs that these experiments dictate. But I have MASSIVE respect for the likes of T20, Bigtoe, Wonky, Jon and Nick.
Not only can they play a wicked tune, but they'll openly share their findings with us.

We've been here many times; long vs short stroke, narrower vs big bore. And you can go with all the chaps' explanations and think, "Yep, that's the definitive way to go", but then see another opposing explanation, agree with that, too, and then be impressed with ALL the tunes and approaches.

For example, I had the undoubted pleasure of trying Wonky's short stroke 80 nearly two years ago, and it was mightily impressive. And now, with further development, he's improved further on this. Mind boggling.

And these forays with 23mm present the next stage of very exciting development.

We're spoilt for choice, it seems, and personal preference will dictate each shooter's choice and, again, we're so lucky to have such skilled people amongst us who will openly share their knowledge.

[slugger]

this whole narrow bore concept got me thinking last night about going as small as possible, but then you are governed somewhat by spring dimentions.......so then i thought about a reversed gasram...
just have the plunger part [as narrow as you fancy] with a piston seal on the end [bit like one of nicks wall-less pistons]
the only thing im strugling with in my head would be how to 'latch' the piston end if its within a sealed reservoir
then i came up with an internal head to do the building of pressure when cocking, a traditional piston rod-end for latching... could work well, entirely tunable for shot feel, but im wondering how much volume is required for the air reservoir [minimum]..

[bigtoe01]

Long and thin should be more efficient, also less pressure to cause (inevitable) piston bounce, hence a lighter piston can be used, which moves faster, less recoil etc. I've high hopes of 23mm

I thought it would have had a higher peak pressure earlier so more susceptible to bounce due to smaller pressure cylinder diameter....we shall soon see, if i get a chance I will swap one of the triggers from one of my 80's (they all have rotating pistons so modified trigger sears) into the 77 over the next 2 days with an LGV spring and see how it does.

Really hoping this works well, very keen on going 23mm in the LGU also if it does, aluminium2buy on the bay stocks 25mm od 1mm wall in short lengths. To date i have never been happy with the LGU, its a fine gun but not a patch on my TX now, if the 77 is transformed with this 23mm conversion it will just have to happen in the LGU also along with a new trigger blade.

[NickG]

I thought it would have had a higher peak pressure earlier so more susceptible to bounce due to smaller pressure cylinder diameter....we shall soon see, if i get a chance I will swap one of the triggers from one of my 80's (they all have rotating pistons so modified trigger sears) into the 77 over the next 2 days with an LGV spring and see how it does.

Really hoping this works well, very keen on going 23mm in the LGU also if it does, aluminium2buy on the bay stocks 25mm od 1mm wall in short lengths. To date i have never been happy with the LGU, its a fine gun but not a patch on my TX now, if the 77 is transformed with this 23mm conversion it will just have to happen in the LGU also along with a new trigger blade.

I am not impressed with the lgu either, I think the firing cycle is far too slow, I am going to short stroke mine with a simple head extension, and maybe a snappier spring, and yes you guessed it I will be using an o ring, though I am very impressed with the shot feel of the new hw seal.

[bigtoe01]

I am not impressed with the lgu either, I think the firing cycle is far too slow, I am going to short stroke mine with a simple head extension, and maybe a snappier spring, and yes you guessed it I will be using an o ring, though I am very impressed with the shot feel of the new hw seal.

I went the other way, i managed to pick up an early 7.5j LGV piston, which is modular, so I was able to shorten the rod and push back to 80mm stroke keeping maximum spring room. I wish I could find a source of true 7.5j pistons as they work beautifully in Diana rifles also.
One area I partially looked at (thinking about it now) is piston weight, i should push it down more as i now favour 200g where the LGU is at 230g right now. There is a possibility this is all I will need to do, although im kinda hoping 23mm is the way forward.

Annoys me we can only buy the 16j piston service kits, i would probably buy 2x more 7.5j kits than the 16, i have already worked thru over 50 16j kits now.

[NickG]

I went the other way, i managed to pick up an early 7.5j LGV piston, which is modular, so I was able to shorten the rod and push back to 80mm stroke keeping maximum spring room. I wish I could find a source of true 7.5j pistons as they work beautifully in Diana rifles also.
One area I partially looked at (thinking about it now) is piston weight, i should push it down more as i now favour 200g where the LGU is at 230g right now. There is a possibility this is all I will need to do, although im kinda hoping 23mm is the way forward.

Annoys me we can only buy the 16j piston service kits, i would probably buy 2x more 7.5j kits than the 16, i have already worked thru over 50 16j kits now.

You obviously like those pistons !, I was also thinking lighter weight, along with the spring, got to watch cocking effort though.

I am only experimenting as there is no point in making it into a TX I already have two of those, I will probably move it along once I know what's going on with it

[Shed tuner]

One area I partially looked at (thinking about it now) is piston weight, i should push it down more as i now favour 200g where the LGU is at 230g right now.

I seem to remember having that argument with you 6 months or so ago... good to see we're all on the same page now

Looking forwards to trying that 23mm HW of yours, hopefully I'd have had time to do a 23mm TX by then

[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 ?