Deciding On Spring Length And Spacing...

[Hsing-ee]

How do the tuners and re-engineers decide on the spring they put in their rifle or rifle kit? A short spring with lots of spacing, or a longer softer spring with just a guide and top-hat - or a maybe a long stiff spring and hope it doesn't jolt too much? Or is it done by 'trial and error'? My experience is limited to comparing the short stiff V-Mach spring to the longer softer Weihrauch spring in the 77 ... both have their merits in terms of the recoil characteristics. Is there a rough equation? I know the transfer port size and volume and the weight of the piston will be big factors, but where do people start with springs?

Just got a rifle that has a longer stroke & more spring-room than its modern equivalent, the modern spring fits but a longer spring could be fitted in ... should I just space the modern spring or modify a longer spring to fit? Or is it a case of suck it and see?

[slinger69]

Jim Tyler ( BTDT on here) wrote a very useful article in September's 'Airgun World' that addresses most of your queries.

[Hsing-ee]

Jim Tyler ( BTDT on here) wrote a very useful article in September's 'Airgun World' that addresses most of your queries.

Of course, the Lord of the Springs would know. I will try to find a copy. Thanks.


Hmmm.... none on the bay and for some inexplicable reason the downloadable version is not available for purchase, most odd and contrary to the laws of capitalism.

I shall have to put a wanted ad up...

[bigtoe01]

I tend to not get to technical about choosing a spring, i start with the spring room, weight of piston and calibre. Something like a 77k in .177 at 80mm stroke will usually end up with 32 coils 235 to 240mm spring, sometime 31 coils, wire can vary from 3.1 to 3.3mm. Now this is a lot softer than a V-mach spring and usually a little longer. On an old HW50 or 55 a 200mm spring, I forget the coils but the wire is 3.15mm, i have tried a shortened LGV spring in a 55 and it worked very well but the dia was a little to large. I tend to look for 30 to 40mm preload as a rule of thumb.

Most springs i play with here on say TX's, 77's, LGU etc are all the same, I found what I like and just stick with it

For D52's 54's etc I just use the stock 16J Diana spring, its excellent, i reduce the power it will develop by reducing the swept volume (a lot)

What I did find is .22 to .177 can need anything from 5mm to 10mm more length on spring same coil count...so .177 spring has way more energy. However i get round this by altering stroke so the .22 will use the .177 spring but the piston will not go back as far Plus adding a mad spring on a short stroke gun usually just ruins it or makes it favour heavy pellets. So when i order my springs now they are pretty much all the same spec.

[Hsing-ee]

I tend to not get to technical about choosing a spring.... . I tend to look for 30 to 40mm preload as a rule of thumb.

Thanks very much Tony, that is what I need, just a starting point to experiment with.

[bigtoe01]

Thanks very much Tony, that is what I need, just a starting point to experiment with.

what you do is build the gun with no spring and work out the compressed spring room, this decides what coil count you can have and wire thickness.

[wonky donky]

I do something similar to Bigtoe01, however I use 3 wires, 2.95, 3.2 & 3.25 ( I do have others) but 2 diameters, 12.87 & 14.2 i/d.

What I have found is depending upon a number of things, too many to go into, power is often a moot point, firing cycle is the deciding matter.
As an example take a short stroked MK3 Tx200. .177 Stroke 83mm Vortek seal I can use a 2.95 wire x 12.87 i/d spring with 29 coils & get 790 + fps with 8.44gn pellets (lots more if I wanted) & the Energy will be comparable with lighter variants.

Okay now a seal change to a 25mm HW..40fps loss of Vo so one extra coil needed.

Change the seals again to an LGU seal & no way can I get power so I change to a 3.2 wire probably about 31/2 coils 14.2 i/d & power restored. I know, strange because I can get high FAC power with a 2.95 wire spring which I have up to 35.5 coils.

As an aside I have had the same conversation with Tony & Brian Samson who both say they have power gains with the LGU seal not losses. I don't know about Brian but I do know Tony uses the 3.2 wire spring in his TX200....I'm now looking deeper & have a meeting with my spring manufacturer.
I deliberately didn't buy AGW to look at Jims article when TonyL announced it as I was doing some spring research at the time.......now I've finished I can't get one!

HW80 .22 short stroke to 68mm. No way can I get power with the above spec springs no matter how many coils but 3.25 wire with 30 coils does the trick.

Now let me explain further, all my springs have the same coils spacing within a Gnats whatsit. They are all based on 33 coils with a free length of 240mm although I have them made up to 35.5 coils.

I keep getting asked for springs to do this & that so I have experimented with standard stroke rifles using my springs to save cost. What I have now found is two springs will both do the same job in the same rifle except for calibre.

Also same spring, same rifle .22 one coil less than .177 every time in the tests I've done.

So other than the variable you normally encounter what's key? IMHO BORE DIAMETER!

[Hsing-ee]

I do something similar to Bigtoe01, however I use 3 wires, 2.95, 3.2 & 3.25 ( I do have others) but 2 diameters, 12.87 & 14.2 i/d.

What I have found is depending upon a number of things, too many to go into, power is often a moot point, firing cycle is the deciding matter.
As an example take a short stroked MK3 Tx200. .177 Stroke 83mm Vortek seal I can use a 2.95 wire x 12.87 i/d spring with 29 coils & get 790 + fps with 8.44gn pellets (lots more if I wanted) & the Energy will be comparable with lighter variants.

Okay now a seal change to a 25mm HW..40fps loss of Vo so one extra coil needed.

Change the seals again to an LGU seal & no way can I get power so I change to a 3.2 wire probably about 31/2 coils 14.2 i/d & power restored. I know, strange because I can get high FAC power with a 2.95 wire spring which I have up to 35.5 coils.

As an aside I have had the same conversation with Tony & Brian Samson who both say they have power gains with the LGU seal not losses. I don't know about Brian but I do know Tony uses the 3.2 wire spring in his TX200....I'm now looking deeper & have a meeting with my spring manufacturer.
I deliberately didn't buy AGW to look at Jims article when TonyL announced it as I was doing some spring research at the time.......now I've finished I can't get one!

HW80 .22 short stroke to 68mm. No way can I get power with the above spec springs no matter how many coils but 3.2 wire with 30 coils does the trick.

Now let me explain further, all my springs have the same coils spacing within a Gnats whatsit. They are all based on 33 coils with a free length of 240mm although I have them made up to 35.5 coils.

I keep getting asked for springs to do this & that so I have experimented with standard stroke rifles using my springs to save cost. What I have now found is two springs will both do the same job in the same rifle except for calibre.

Also same spring, same rifle .22 one coil less than .177 every time in the tests I've done.

So other than the variable you normally encounter what's key? IMHO BORE DIAMETER!

Fascinating stuff. With the calibre issue, is it actually the volume of air behind the pellet that is the issue, or rather the weight and the friction holding the pellets in the breech that is the issue? Have you tried any pellet seating experiments? In The Airgun Book, John Walters tried seating pellets at different depths and tried accuracy and power tests ... there were some 'sweet spot' depths that improved both power and accuracy. Obviously seating too deeply will cause a bit drop in power, but there seemed to be a narrow range of seating which could influence power to a significant degree, up to 1 fpe difference. Seating would also be affected by the TP as it increases the dead-space behind the pellet while reducing friction at the same time ...

I dont know how you are not driven completley mad by all the variables!

[TonyL]

All brilliant stuff, chaps.

Jim's articles were excellent and I'm sure might be available via ordering back issues?

I like Tone's "non-too scientific" approach - saves a little headscratching!

One thing, with the recent leaning towards longer / softer springs, that stood out very recently was how lovely Gwyn's HW95 was with the SFS spring. Snoops posted specs on the mainspring thread. A shorter, stiffer spring, very little static preload (16mm ish, I think) and it shot beautifully.

Horses for courses, I suppose, backed up by Tony and Dave's findings up above.

And yes, Al, absolutely fascinating, our little spring powered toys. I started a thread quite some time ago and, by large, most commented that seating very often, didn't help. But, as you say, it'll have so much to do with swept volume / dead space / pellet weight and tightness in the breech. Jim's done some fascinating articles on pellet release pressure, pellet release at specific points in the firing cycle etc.....

[wonky donky]

All brilliant stuff, chaps.


One thing, with the recent leaning towards longer / softer springs, that stood out very recently was how lovely Gwyn's HW95 was with the SFS spring. Snoops posted specs on the mainspring thread. A shorter, stiffer spring, very little static preload (16mm ish, I think) and it shot beautifully.

..

That really surprised me Tony as I have taken two SFS tuned 95's apart & sure the springs I looked at, although the same, were different dimensions to the one John measured.
I keep meaning to dig them out but keep forgetting.

[Shed tuner]

My process... (not read all the other replies)

Chuck in any spring of about the right size
Change them around until you get one that makes makes about the right power.. (anything from 9.5 to 13) you now have a baseline.
See if the gun is tending to slam or bounce by testing with light heavy pellets
If over powered, and slammy, you need a shorter spring
If under powered and bouncy, you need a longer spring
if over powered and bouncy, you need a longer (to reduce the bounce), weaker (to reduce the power) spring and maybe a heavier top hat / larger port
if under powered and slammy, it's more complex... if you are lucky it might just be over sprung - find a less powerful spring. Or the piston might be too heavy. Or the port might be too big (e.g. B2).

Essentially everything is then iterative from there.

I try not to have more than minimal spacing, as I find active spring length beneficial to shot cycle. I threw Macarri's short spaced spring out of that FWB

Spacing does work when you NEED a short stiff spring, i.e. when the gun is wanting to slam (piston too heavy, port too big) - but much better to address the underlying reasons (lighten the piston, sleave the port) than to resort to 1/" lumps of plastic reducing spring room
HTH - JB

[Hsing-ee]

Thanks Jon, brilliant, I can draw out a flow diagram based on what you have written and start 'iterating'! I think the old Maccari spring can be re-used as a 77 or 95 spring if it hasn't be cast into the scrap skip at Merton recycling. It wasn't cheap!

Spacing does seem a bit - well, wouldn't it be better to have spring in there?

[TonyL]

That really surprised me Tony as I have taken two SFS tuned 95's apart & sure the springs I looked at, although the same, were different dimensions to the one John measured.
I keep meaning to dig them out but keep forgetting.

Hi Dave,

Unless they now specify a different spring, maybe?

Only had time for a very brief look-in this morning before work and forgot to add that the spring in the 99 you supplied me with is spot on.

Loving this thread......

[Shed tuner]

Thanks Jon, brilliant, I can draw out a flow diagram based on what you have written and start 'iterating'! I think the old Maccari spring can be re-used as a 77 or 95 spring if it hasn't be cast into the scrap skip at Merton recycling. It wasn't cheap!

Spacing does seem a bit - well, wouldn't it be better to have spring in there?

Of course kept the spring Will be fine for a shorter cylinder gun, or a .22

[rojin]

How do the tuners and re-engineers decide on the spring they put in their rifle or rifle kit? A short spring with lots of spacing, or a longer softer spring with just a guide and top-hat - or a maybe a long stiff spring and hope it doesn't jolt too much? Or is it done by 'trial and error'? My experience is limited to comparing the short stiff V-Mach spring to the longer softer Weihrauch spring in the 77 ... both have their merits in terms of the recoil characteristics. Is there a rough equation? I know the transfer port size and volume and the weight of the piston will be big factors, but where do people start with springs?

Just got a rifle that has a longer stroke & more spring-room than its modern equivalent, the modern spring fits but a longer spring could be fitted in ... should I just space the modern spring or modify a longer spring to fit? Or is it a case of suck it and see?

Dont cut a spring down,horrible really. Dia of wire is very important,I use a spring with less coils to get a faster action in my prosport but becareful not to go over the legal limit with a lesser coil amount.