Short stroking vs sleeving?

[greenwayjames]

"the old articles are what i like being honest"

A long while ago now he told me that some of the articles were "misleading" when it came to how things actually were. I have noticed some of the discriptions can be a little vague. I suppose it was understandable as that was his business.

[bozzer]

I've always wanted to give a 48/52 a good go at HFT in a custom stock.

I was always worried about a 24fp rifle running at 12fp and didn't think the trigger was in the Rekord class. This downsizing the internals to give 12fp and the new trigger makes it a decent option.

I was scoring well with the 25mm 77 last winter and then got lost in a world of zero shifts ( or me just shooting sh1te ). The 77 is going down the FT route. I was going to go pcp in HFT but maybe this winter I'll get hold of a 48/52 and give it a try.

[wonky donky]

Just come off the phone after a long chat to JB about reduced bore size air rifles. He said that was the way ahead and he convinced Gamo the Hunter 1250 was not the ideal way to go for US markets. The 52 that was tested had the stroke shortened by about an inch as well as the cylinder being sleeved. The gunwriter wanted to do a back to back test against a 52 that another well known designer had done his conversion on. That person favoured lighter pistons but Bowket heavy. The magazine apparently said no. He told me he made a scratchbuilt air rifle with a 7/8" bore and stroke about 3 3/4" which showed promise but that was superceded by a rather different approach to reducing the front area of the piston to gain the benefits. This design was sketched out in one of his AGW articles and the result was a call from Fredrik Axelson saying he was trying to sell the same layout to a well known, now defunct, gunmaking company. I found that amusing, a case of great minds thinking alike. Quite an interesting and informative chat.

I had the very same conversation with John a couple of months back, he also told me Gerald Cardew didn't agree with his Johns view regarding added piston weight and thought like the other Designer/Tuner lighter pistons, to a point, were they way forward.

Myself I have to agree with Gerald Cardew & Tony (Bigtoe01) for sub 12fpe rifles.

The other thing to note is when John did his 12fpe modifications on the BSA Meteor he brought the piston weight from about 175gms to the magic numbers of 220/250gms

[TonyL]

Most people's perception is that at 12 ft/lbs the HW80 is particularly understressed, resulting in excellent reliability.

It is the 'desert island' gun of choice for many people.

Yes, as above.
The gun is built like the proverbial brick outhouse, mega reliable and a doddle to strip.

In standard, lazy, layout, they can still be very accurate. But much sweeter once stroked (with lighter piston) or sleeved.

As I've already commented on other related threads, Wonky Donky's short stroked, lighter piston with buttons 80 is an absolute joy to shoot.

All the sleeved ones I've tried are very impressive.

As Tone stated further up, hype, marketing and a lack of availability of "magnum" air rifles at the time of launch helped the 80 achieve huge success in its day. All helped, no doubt, by it's heft, further reinforcing its "strong build and power output".

It always was a superb rifle, is still a very viable choice today, even in standard form, but can be made much more refined.

[steve m]

Most people's perception is that at 12 ft/lbs the HW80 is particularly understressed, resulting in excellent reliability.

It is the 'desert island' gun of choice for many people.

i cant stand the german junk
steve

[Shed tuner]

Stroke vs bore...

So given the same volume (say 40cc) and the same piston weight (say 225g), what's the optimum bore ?

I'm thinking that the larger bore will have less mechanical advantage in getting the pellet moving than the smaller, hence smaller = better, subject of course to practical limits on spring / cylinder length. But there must be an optimal solution here....

[greenwayjames]

"The other thing to note is when John did his 12fpe modifications on the BSA Meteor he brought the piston weight from about 175gms to the magic numbers of 220/250gms [/QUOTE]"

I know nothing of "magic numbers" but if I remember my schooldays correctly altering piston weight from about 175gms to 225/250gms is adding to its weight
BTW. JB was the first to use what are now called tophats, but his were in steel to add weight

[greenwayjames]

i cant stand the german junk
steve

I agree, Terrible. What with barrels breaking off breechblocks, triggers that dont work, low or too high power, poor finish and general lack of quality control. Whatever next

[bigtoe01]

Stroke vs bore...

So given the same volume (say 40cc) and the same piston weight (say 225g), what's the optimum bore ?

I'm thinking that the larger bore will have less mechanical advantage in getting the pellet moving than the smaller, hence smaller = better, subject of course to practical limits on spring / cylinder length. But there must be an optimal solution here....

25mm will be 80mm stroke
26mm will be 74mm stroke
28mm will be 65mm stroke

all 3 would work, however the 28mm may feel a little snappy, so you would need to lengthen the stroke to at least 70mm and go with a softer spring with more preload (longer spring)

25 and 26 would feel very very similar, to get 26 nice slightly softer spring with added preload.

25 is optimum right now, but anything in the 70 to 80mm stroke ranger works apart from 30mm that starts to feel lazy and must be around 70mm stroke and 250g

[wonky donky]

"The other thing to note is when John did his 12fpe modifications on the BSA Meteor he brought the piston weight from about 175gms to the magic numbers of 220/250gms

"

I know nothing of "magic numbers" but if I remember my schooldays correctly altering piston weight from about 175gms to 225/250gms is adding to its weight
BTW. JB was the first to use what are now called tophats, but his were in steel to add weight[/QUOTE]

Yes weight was/is added.....Sorry didn't go into detail as I assumed (wrongly it seems) people would know pistons can be too light as well as too heavy! Apologies

I don't know about being the first but you are correct about using Top Hats to add weight to the piston.

The point I'm trying to make is Johns Meteor conversion is similar in many ways to what some of us tune to at the moment for sub 12fpe hence the magic numbers statement.......if that makes sense?

[bigtoe01]

I personally think many have took adding weight and applied this to all pistons...this is bad. A Diana piston weighs 300g, an 80 Piston weighs 330g...toooooo heavy for sub12. Now a HW55 piston weighs 165g, an old 50S piston weighs 175g or so....this is to light for uk 12

So JB may have been adding weight to light weight pistons but not all pistons, i do know he added weight to the 25mm 77k piston however..i tried it and found it too thumpy as its was too heavy, we tried his FT rifle at the boinger bash (Solware let us test it) and while i thought it not to bad a few thought it way to thumpy...

The magic range is 220 to 250g for sub12 depending on spring room...a new 97k piston weighs more than this and a good tune will lighten the piston down, 20 to 25g off and a stroke reduction gets the feel just like a 25mm piston gun

[greenwayjames]

"So JB may have been adding weight to light weight pistons but not all pistons, i do know he added weight to the 25mm 77k piston however..i tried it and found it too thumpy as its was too heavy, we tried his FT rifle at the boinger bash (Solware let us test it) and while i thought it not to bad a few thought it way to thumpy."

I wonder when that was last serviced and by whom. I have tried to get JB to do one of his springer conversions and he told me the last one he did was about 20 years ago. The ones I had done were all incredibly soft shooting even the ones I had on FAC. He did say that once the piston had been taken out the special head he fitted was no good for further use. When he serviced them he made another for that particular airgun.
BTW he was the first to do Delrin spring guides too

[bigtoe01]

"So JB may have been adding weight to light weight pistons but not all pistons, i do know he added weight to the 25mm 77k piston however..i tried it and found it too thumpy as its was too heavy, we tried his FT rifle at the boinger bash (Solware let us test it) and while i thought it not to bad a few thought it way to thumpy."

I wonder when that was last serviced and by whom. I have tried to get JB to do one of his springer conversions and he told me the last one he did was about 20 years ago. The ones I had done were all incredibly soft shooting even the ones I had on FAC. He did say that once the piston had been taken out the special head he fitted was no good for further use. When he serviced them he made another for that particular airgun.
BTW he was the first to do Delrin spring guides too

dont forget he boiled delrin to strengthen it there are MUCH better materials now however, but they obviously cost more. I use Acetal H that is not delrin branded (same stuff) but have now started experimenting with Ertalyte TX which is PET, it is stronger, does not suffer from moisture ingress, has a lower coefficient of friction and is way more temperature stable than POM...and it machines lovely

Regards who serviced the 77, no clue, it was a dual O ring short stroke job, and why he changes the head...something being changed there as you would just change the O rings on a service not the whole head

[Burg308]

I am the lucky chap who owns the pro sport mentioned in a earlier post ,I shot the gun again tonight,it is
Absolutely fantastic in comparison to its original AA factory spec,so easy to shoot all the hold sensivity has
Gone,accuracy with daystate select is as good as pcp I own ,and I own a few.I think it's time we showed our
Appreciation for the likes of big toe and wonky who have taken the job of tuneing a springer into a science,
These guys are so open with their knowledge it gives the average shooter the ability to own a gun that is as
Good as it should/could have been from the factory.

[Captain Bongo]

These guys are so open with their knowledge it gives the average shooter the ability to own a gun that is as
Good as it should/could have been from the factory.

Well said. I learned an awful lot just from listening to Bigtoe and others at the springer event. My own Prosport is now running very sweetly with a MK1 TX piston. I had tried this conversion earlier in the year with poor results, but the free flow of advice available in that field has helped me transform a good gun into my own personal dream gun.