A New Method for Increasing the Efficiency of a PCP - the SSG

[rsterne]

The 13XX spring is the same length as a Disco spring, but smaller wire.... The 2200 spring is the same wire as the early Disco spring, but longer.... I have no idea what the new Disco spring is.... I think the ideal spring for a stockish Disco might be one like a longer 13XX spring, but don't know of, or have one, currently.... I would look for something about 0.032-0.033" wire and 2.5" long.... Since the springs are riding on a close fitting rod (in my SSGs), you can also use two springs (with closed ends) butted together.... You should be able to use two 13XX spring, with a total length (after being set, so they don't get any shorter) of about 2.5" uncompressed, preloaded about 3/4"-1" (roughly).... Another alternative might be two of the original Disco springs, with a total length of about 2.3-2.5" (after being set), with 1/2-3/4" preload (roughly).... If you use longer springs, of course, you will need a custom end cap / adjuster bolt further back.... Sorry this is still in it's infancy and no set answers are available....

Bob

[Rivers3Plinker]

The 13XX spring is the same length as a Disco spring, but smaller wire.... The 2200 spring is the same wire as the early Disco spring, but longer.... I have no idea what the new Disco spring is.... I think the ideal spring for a stockish Disco might be one like a longer 13XX spring, but don't know of, or have one, currently.... I would look for something about 0.032-0.033" wire and 2.5" long.... Since the springs are riding on a close fitting rod (in my SSGs), you can also use two springs (with closed ends) butted together.... You should be able to use two 13XX spring, with a total length (after being set, so they don't get any shorter) of about 2.5" uncompressed, preloaded about 3/4"-1" (roughly).... Another alternative might be two of the original Disco springs, with a total length of about 2.3-2.5" (after being set), with 1/2-3/4" preload (roughly).... If you use longer springs, of course, you will need a custom end cap / adjuster bolt further back.... Sorry this is still in it's infancy and no set answers are available....

Bob

Great info - thanks Bob!

[rsterne]

Lloyd, great to see your rear cocking SSG is taking shape.... and I look forward to your tests.... I have one piece of info you (and others) will find helpful.... The hammer needs AT LEAST the same energy it had originally to do its job.... but now the spring is accelerating extra weight.... so the hammer is going slower (if you don't increase the spring energy), plus it has to coast while in contact with the valve.... You need to get that hammer velocity back with more spring energy.... In Lloyd's case, not very much extra (a thin tube, he already had the cocking rod).... in the case of my 37 FPE 2260 HPA a bit more, because although it had a spring guide (that helped the hammer strike), now that guide is no longer part of the hammer energy (it stops before the hammer hits).... If your original hammer used a short, stiff spring, the hammer was already coasting the last bit, but now you have added all the mass of the guide to the system.... and in the worst case (the normal one for most PCPs), where you had a preloaded spring pushing the hammer the entire cycle, now you added the weight of the guide, PLUS the hammer is coasting all the time it touches the valve.... I haven't put any numbers on it yet, but I'm thinking you need to increase the total spring energy stored by 20-50%.... most of which is the preload in the spring....

Bob

[pllagunos]

Lloy, could you explain the function of that rod? I am getting lost in so many info lol  good work guys!

Sure thing.  The Disco has that cheesy little bolt handle that locks the bolt into the breech but also pulls the hammer back via an offset little pin, and also compresses and cocks the spring.  In a stock Disco with a light weight hammer spring, that arrangement works just fine.  But if you want more power, that usually means (among other things), a stiffer spring.  Sometimes the little bolt handle is not up to the task and breaks, or the hammer tends to bind from being pushed cockeyed against the spring.  The new cocking rod is threaded straight into the hammer, thru the middle of the spring, so that you can pull the spring straight back, without any side loading, and without putting undue stress and wear and tear on other parts of the system.  The cocking rod idea has been around for a long time and helps a lot for higher power versions of the Disco, and similar design guns.
Lloyd

Now I get it, thanks!

[Motorhead]

Im starting to hate all you guys especially Bob for starting this and Lloyd for feeding the fire and Scott for doing it, That's it I do hate all you uns.  David

David,
Come on in, waters warm and beers cold.
Sittin on side line "Haten" is non productive .... Get out in the shop and Make sum thing !!!

[ped]

just like to thank you Bob for sharing this innovative concept and all you other chaps for sharing your work and variations of it
once I get a bit of time I'm going to knock one up in the man cave and see how it works with sub 12fpe(sadly our limit)and co2

[Motorhead]

Found a great setting on the .22
Knew I had a 10# spring someplace, just needed to find it !
Took hammer spring preload to full soft, cut down the Hats spring shoulder some as well to take hammer spring to less preload.
Over onto the chrony ... 920 fps with 18.1's WOWZER we have some power now !
Dismantled and took some more off the hats spring shoulder further reducing preload by @ .080"
Back together testing again ... 895fps & PERFECT !

Cocking effort just a tad stiffer with the 10# spring with @ 3/8" preload than the 6# at near coil bind.  In terms of cocking effort really no big deal.
So what this does ADD to Bobs original thoughts about softer springs with a LOT of preload, is that a stiffer spring with less works too 

Side benefit tho not proven as of yet ... with the heavier spring fitted the speed of hammer strike actually gets valve open quicker, tho because hammers coasting poppet closes just as quickly.  DWELL does seem to have decreased listening to muzzle report becoming crispier/snappier sounding 

Scott

[oldpro]

Ok I'll play lol http://i.imgur.com/8N4xqpzh.jpg  http://i.imgur.com/mrYhQfEh.jpg  http://i.imgur.com/zZjxC0lh.jpg  http://i.imgur.com/G9PyCWRh.jpg Good start I think. I can preset hammer spring tension and then set how much float I want.

[Tomg]

I knew you would Travis! (I can't keep you two apart) That and the fact I talked with Jim yesterday about the SSG....lol

Let us know what you find on the Flex.

 

[Motorhead]

Ok I'll play lol http://i.imgur.com/8N4xqpzh.jpg  http://i.imgur.com/mrYhQfEh.jpg  http://i.imgur.com/zZjxC0lh.jpg  http://i.imgur.com/G9PyCWRh.jpg Good start I think. I can preset hammer spring tension and then set how much float I want.

Travis ... welcome

[oldpro]

 The FLEX already has a similar system in place. This does however look to be a great upgrade for many air rifles.

[Matt15]

I got the gauge for my .25 pumper, Bob. I have not had time to install it. I will be doing the SSG to my gun also.

Will I  need a heavier hammer spring or a lighter but longer spring? Thanks Bob!!!

[Motorhead]

On another note & question for Bob

In terms of strike energy stored in springs AND THE LONG TERM CONSISTENCY .... 
would not a spring spending most of it's life with a LOT of preload, then stressed to near coil bind when cycled have a SHORTER LIFE and suffer from SACKING OUT much faster than a slightly stiffer spring with far less preload while being nowhere close to coil bind when cycled ?
Where as shown in a earlier chart, BOTH exhibit close to the same energy as differing preloads.

Thinking too much .... my bad .

Only asking this for terms of LONG TERM CONSISTENT setting having fitted AG be less finicky over time.

[PakProtector]

I am working the bits similar to Travis, only with a 3"an push the preload up, leave minimum amount of spring/guide adjustment. Going to turn a bit for the OE Marauder endcap in 9/16-20 for the float, and a guide of Aluminum turned to .25"( for 1/4-28 nuts ). Will try a .062" wire spring first; around 17 lb/in or so. I hope to get the .224's valve well open at 3k psi...as I have never gotten the highest power out above 2k7 psi.
cheers,
Douglas
--this will run the A7 sear...

[Gerard]

Motorhead; as I understand from some of the more experienced, engineer-type contributors on various firearms-related forums, fear of magazine springs getting weaker is primarily a worry of those less experienced. Many have said that it's not static compression which bags out springs, it's cycling. So those who obsessively empty and fill their magazines are the ones most likely to see springs getting weaker. Leaving mags loaded for years is like loading them once, no matter how long they're stored, provided there's a bit of oil and the springs don't rust... but that degrades the springs in either compressed or uncompressed state so not really relevant.

That said, I've seen the odd airgunner saying that leaving a break-barrel or other spring-piston air rifle cocked for long periods weakens the mainspring. So I'm not completely certain who to believe... though the expertise among the firearms guys has generally seemed deeper where the anecdotal stuff about springers has been a bit less informed-sounding.

[rsterne]

Scott, I have no doubt that the SSG will work with (relatively) shorter stiffer springs, providing you can get the travel you need without hitting coil bind.... I'm not so sure why it would give increased hammer velocity, though, because if it did, your power would go up, assuming you weren't on the velocity plateau.... In theory, at least, all setups that produce the same hammer velocity at the valve (when the guide stops), and have the same hammer stroke, would require the same average spring force.... It shouldn't matter if you start with 0 lbs. force uncocked and go to 20 when cocked.... start at 5 lbs. and go to 15.... or start at 9 lbs and go to 11.... the average force is 10 lbs, and if the guide moves 1.2" that is 1 FPE (10 x 1.2 = 12 in.lb) of energy.... What is likely happening is that when you use a stiffer spring, you are using a larger gap, and as you lengthen the gap, you shorten the compression, to make up for that higher average force.... ie you are flinging the hammer at the valve from further away.... The thing that will happen, if, for instance you use the stock spring and preload it, is that you will increase the cocking force by the amount of preload.... Some guns, that won't matter, on my Grizzly, for example it wasn't acceptable to increase the cocking force even further....

My experience with springs is that once they are "set".... ie fully compressed to coil bind.... they don't change, at least I have never seen it.... I always set my hammer springs before installing them the first time.... ALWAYS.... The first time I increased the preload on a Disco hammer spring until I hit coil bind, as soon as I backed it off I got lower velocity readings than before.... I took the spring out and measured it, and it was over 1/8" shorter than when new.... Recorded all the preload vs velocity data with the shorter "set" spring and never had it change again....

The data I have seen on leaving Springers cocked is that they lose about 1% a week for the first month, then 1% a month for a few months to about 10-15% loss, then stay that way.... and I'm betting they didn't bother to set the spring before they started their measurements.... Seriously, I really doubt the hammer spring getting weaker with time is an issue, PROVIDING you set the spring to coil bind (I do it maybe 10 times in quick succession) before installing it.... The preload on the SSG will be only about 1/3-1/2 of the force at coil bind anyway....

Travis, welcome aboard.... I look forward to hearing your results.... This, for me, is exciting....

Bob

[Motorhead]

Scott, I have no doubt that the SSG will work with (relatively) shorter stiffer springs, providing you can get the travel you need without hitting coil bind.... I'm not so sure why it would give increased hammer velocity, though, because if it did, your power would go up, assuming you weren't on the velocity plateau.... This, for me, is exciting....

Bob

In this rifle with the 6# spring at coil bind when cocked maxed out at 835 fps with 18.1's
Going to the 10# spring ( Same OAL ) took preload down to 1/4 of what it was.
so we do have more spring energy at hammer obviously being velocity jumped up to +/- 900fps with same pellet.
also where the hammer speed came from no doubt.  Odd part is & why noting it, even tho power jumped up the noise really did not, actually becoming sharper/crisper without really seeming louder.

Anywho ... Thanks

[PakProtector]

Scott, how did you get a 6# spring to coil bind in a Marauder?
cheers,
Douglas

[Rallyshark]

I didn't say I was going to convert EVERY PCP I have.... *LOL*.... Yes, the AT-44 could be quite a challenge, and since it already has an anti-bounce device, may not be worth it....

Bob

Along with the fact diameter of hammer spring is so small .... getting the energy to valve could be troublesome

You guys are no fun, lol!  I would like to come up with something, because that anti-bounce "device" is taking a beating at 55fpe I think... That is part of the reason I want to come up with a damper/hammer set up. I can adjust the bound \rebound independently, and I think it would work if I get it right.  I suppose a damped hammer stop could be another way to approach it too. I just don't think that anti-bounce device is living up to the gun's potential.  Its using a lot of air, and making some noise at that power level.  I have a few different ideas, but I need to order some spare parts, before I go down that road  

I also feel like I could do it with a factory spring without that hammer stop there.  My internet is down, and I'm on 4G right now, so I can't do any show and tell, but I WILL come up with something.  It will take me longer than you guys though. Just a little background on me, so you don't think I'm completely crazy, but I have done formula BMW race engineering, and SCCA stuff.  I say that so you guys understand I have no shortage of ideas on how to do it. The damper \spring set up on those formula cars gets pretty crazy. No, I'm not going to put cantilever suspension on my gun, ha-ha! 

I'm really learning and enjoying the heck out of this discussion either way though!

[Motorhead]

Scott, how did you get a 6# spring to coil bind in a Marauder?
cheers,
Douglas

Preloading the rear cap to the max then spacing it further via the hat on stop rod down in hammer cavity.
Together coils get to coil bind when cocked ....