One for the spring tuners - Tom G experiments with preload

[TonyL]

Okay, we know he might not be the most technically advanced but he certainly has the enthusiasm and inquisitive nature. A fairly rudimentary illustration right now on Tom Gaylord's Pyramydairblog where he takes a Marksman 70 and removes some coils from the canted spring. Then some more, then more still, then adds preload spacers to compensate. He also shows a handy little chart documenting muzzle velocity vs cocking effort at each step. And the next step will be a new spring with plenty of fresh, live coils. It illustrates quite nicely the relationship between various factors and the shortening affecting stiffness etc.

Well worth a read.

And he's also recently done a fairly in-depth review / tune / accuracy feature on the HW30S and has just started one on the HW50S/99.

[Geezer]

Quite interesting. Does this mirror what others have experienced?

https://www.pyramydair.com/blog/2021...rifle-part-11/

[Shed tuner]

indeed. spacers aren;t springs - they don't give up any energy... so chopping an inch off a spring and then adding an inch of preload, will not get you back to where you started you also end up with a stiffer spring.

[cjos16]

Sorry for being off topic but that mosin negant looks like a nice little rifle that’s advertised at the bottom of the page tho ��

[TonyL]

The interesting part for me was after the first "spring cropping" and the resulting increase in muzzle velocity. This could be down to a few, or combinations of, factors? Maybe it was over sprung in its previous (factory standard for the US?) guise? Maybe just cleaning out old, dried up lube and treating it to a refresh made more difference? Did the cant impede performance or just wreck the shooting cycle?

The increase in cocking effort ties in with what Jon has campaigned for a long time, where what is desirable is live, active coils. Not to use preload to make up for larger deficits in power, but to facilitate fine tuning.

[evert]

The increase in cocking effort ties in with what Jon has campaigned for a long time, where what is desirable is live, active coils. Not to use preload to make up for larger deficits in power, but to facilitate fine tuning.

In some guns I've found improvement with shorter stiffer springs.
But personal preference probably plays a part in it too.

[evert]

The interesting part for me was after the first "spring cropping" and the resulting increase in muzzle velocity. This could be down to a few, or combinations of, factors? Maybe it was over sprung in its previous (factory standard for the US?) guise? Maybe just cleaning out old, dried up lube and treating it to a refresh made more difference? Did the cant impede performance or just wreck the shooting cycle?

People on the Swedish forum used to advocate cutting a couple coils off the HW50/99 full power OEM spring, and reported power increases.
Never tried it myself.

[look no hands]

I've always tried to keep as much spring as possible when respringing my rifles, but the Welsh Willy kits I've used seem to have slip washers for the ends of the springs (one goes on the spring guide and one goes under the top hat) and also three different size preload washers in Delrin as well, his kits certainly seem to work for me, so may be there's something in it.

Pete

[madcarlos]

Back a while ago I fitted a kit which had very little preload , The spring that was fitted with the guide could not be seen above the top of the action, The trigger block of the hw77 could be screwed back on without having to apply pressure, Did have 3 0r 4 very slim shims, Had to use the 4 but then a while later one by one had to be removed untill it finally settled at 11.1 ftlbs, A while later disaster struck, Something not sounding right, Top hat hat broken, Seems to little preload can cause spring slap, If that's what it's called, As with PCP, Shorter hammer pip or longer, more travel or less travel, Longer or shorter , Harder or softer, Bigger or smaller, It always seems that which ever way you go there is a limit in which the opposite can happen, Back to my top hat, What's your thoughts on what happend.

[Frog]

Back a while ago I fitted a kit which had very little preload , The spring that was fitted with the guide could not be seen above the top of the action, The trigger block of the hw77 could be screwed back on without having to apply pressure, Did have 3 0r 4 very slim shims, Had to use the 4 but then a while later one by one had to be removed untill it finally settled at 11.1 ftlbs, A while later disaster struck, Something not sounding right, Top hat hat broken, Seems to little preload can cause spring slap, If that's what it's called, As with PCP, Shorter hammer pip or longer, more travel or less travel, Longer or shorter , Harder or softer, Bigger or smaller, It always seems that which ever way you go there is a limit in which the opposite can happen, Back to my top hat, What's your thoughts on what happend.

Too little preload and you likely had a load of bounce which is suppressed by preload.
I tend to use the longest, softest springs I can get away with and quite a lot of preload and tune but cutting coils until lighter pellets give a slightly higher power than heavy ones (as long as I am within the UK limit). I do this as my understating is that lighter more power than heavy = piston bounce and heavy more than light = piston slam. A little bounce is better than a little slam.

Shortening a spring does stiffen it - I've used this to tune motorcycle front suspension.

[ajohn]

Spring guns are rather strange things to deal with. I read a pyramidair blog a while ago that explains some basics but can't find it again.

The simple aspect is a compressed spring being released to drive a piston forwards to compress air and fire the pellet. This air gets hot, Preload changes alter power. etc

The pressure the spring can exert gets less as it expands so at some point it can't support the air pressure in front of it. The piston has weight and is moving rapidly so has inertia so at this point will carry on generating more pressure. When that has been used the spring can support even less pressure so bounces backwards. Reducing preload can enhance this effect.

Due to inertia increasing piston weight may increase power.

Then the piston hits the end of the compression tube and the gun recoil is away from the shoulder. Preload can influence that. A lot of the initial recoil is down to accelerating the piston.

It seems that piston weight ideal turns out to be over 200g. Rather a lot more than a7.33gn or more pellet. So I am told anyway after working on a gun that had an added piston weight in the form of a top hat. With the weight it came out 200g plus. Well under without.

The tuners art is balancing the lot. I missed another factor on springs. If shortened and given the same amount of compression the load needed increases as fewer coils are being compressed further. So reducing length when there is preload may not have the desired effect. Suppose it depends on how much preload and coil counts before and after the change. Might only apply on real guns if lots are removed. I also tapered a transfer port very slightly - made a fairly smooth shooting gun go very slamy. Fortunately I could replace it. Same gun didn't behave with preload changes as expected. Large changes did little. This turned out to be due to the wrong pellet. One that could expand more easily gave an extra ft lb+ Seems to be due to a poor pellet fit in the bore of the barrel.

[madcarlos]

Too little preload and you likely had a load of bounce which is suppressed by preload.
I tend to use the longest, softest springs I can get away with and quite a lot of preload and tune but cutting coils until lighter pellets give a slightly higher power than heavy ones (as long as I am within the UK limit). I do this as my understating is that lighter more power than heavy = piston bounce and heavy more than light = piston slam. A little bounce is better than a little slam.

Shortening a spring does stiffen it - I've used this to tune motorcycle front suspension.

Yes seems understandable with a longer softer spring, I will be putting it back together soon and thinking of just getting a standard spring,

[TonyL]

Spring guns are rather strange things to deal with. I read a pyramidair blog a while ago that explains some basics but can't find it again.

The simple aspect is a compressed spring being released to drive a piston forwards to compress air and fire the pellet. This air gets hot, Preload changes alter power. etc

The pressure the spring can exert gets less as it expands so at some point it can't support the air pressure in front of it. The piston has weight and is moving rapidly so has inertia so at this point will carry on generating more pressure. When that has been used the spring can support even less pressure so bounces backwards. Reducing preload can enhance this effect.

Due to inertia increasing piston weight may increase power.

Then the piston hits the end of the compression tube and the gun recoil is away from the shoulder. Preload can influence that. A lot of the initial recoil is down to accelerating the piston.

It seems that piston weight ideal turns out to be over 200g. Rather a lot more than a7.33gn or more pellet. So I am told anyway after working on a gun that had an added piston weight in the form of a top hat. With the weight it came out 200g plus. Well under without.

The tuners art is balancing the lot. I missed another factor on springs. If shortened and given the same amount of compression the load needed increases as fewer coils are being compressed further. So reducing length when there is preload may not have the desired effect. Suppose it depends on how much preload and coil counts before and after the change. Might only apply on real guns if lots are removed. I also tapered a transfer port very slightly - made a fairly smooth shooting gun go very slamy. Fortunately I could replace it. Same gun didn't behave with preload changes as expected. Large changes did little. This turned out to be due to the wrong pellet. One that could expand more easily gave an extra ft lb+ Seems to be due to a poor pellet fit in the bore of the barrel.

The tuner's art is, indeed, to balance the lot. And so much depends on so many inter-related factors on a powerplant that might, outwardly, appear so simple. Like that piston weight at over 200g. That won't suit all guns. Guns with "narrow" bores may well run happier at our power levels with piston weight much, much lower than this. One has to take into account bore, stroke, piston sectional density, its inertia, spring rate, preload, force at rest and cocked (all obviously linked), friction, transfer port volume (and, obviously, its diameter and length) etc.

It's all great fun. For many, if the cocking cycle is smooth, cocking effort considered reasonable, the firing cycle is refined and twang-free, the power is at the desired level, power output consistent and the gun is accurate, it's job done. The masters in this "black art" can, and often do, take things to a higher level.

[Geezer]

https://www.pyramydair.com/blog/2021...rifle-part-11/

[tinbum]

We supply springs over-long as a spring shortened to power (soft) shoots with less cocking effort and piston bounce than a gun at the same energy than a too short spring padded out (stiff) to increase power.
It's simple physics, I had no idea this was news to anyone