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

[Tomg]

Bob, Yes I find the exact same thing, as soon as you have a gap the efficiency is stellar, and as you increase the gap the velocity goes down in a fairly predictable and linear fashion. Which is good as you can use this to fine tune your fps as long as the overall setup is within range of the goal.

RKR: You could use a telescoping center rod with a retaining hat in both ends. However you lose one primary function of the SSG, and that is that the spring system is held firmly in place at the rear, so that the hammer can fly freely to the valve the same way, every time. Retaining the set gap at all times.

I am going to try to make the rear plug in two pieces, an outer shell (metal for the bolts and such) then an inner thinner shell with the rear rod hole in delrin, working as bearing surface for both the spring and the rod going through the rear.

Here is a simple diagram. The (pink) adjuster is a threaded piece and would push on the inner delrin "cup" In the diagram I drew it wrong, i.e. touching the delrin as it's turned all the way in, it would obviously not be that way in the final version.

[rsterne]

If the pink aduster is a larger OD, you can remove the SSG "cartridge" through the hole in the rear cap to work on it, change springs, preload, whatever.... No need for a separate Delrin cup (sleeve).... the spring sits against the end of the adjuster.... a 3/8"-24NF bolt works great for Disco/QB sized springs....

rkr, I see what you are saying, a drop-in package that is a preloaded spring.... That could work, if you can find room for it, but it might preclude going to a longer, lighter spring to ease the cocking force, which is a major advantage.... If you didn't need that, or if you were trying to detune the gun, a drop-in setup that was adjustable for preload should work....

Bob

[Tomg]

If the pink aduster is a larger OD, you can remove the SSG "cartridge through the hole in the rear cap to work on it, change springs, preload, whatever.... No need for a separate Delrin cup (sleeve).... the spring sits against the end of the adjuster.... a 3/8"-24NF bolt works great for Disco/QB sized springs....

Bob

That's a good idea Bob.

[rsterne]

I do all mine that way, if possible.... even my Hayabusa with 1/2" OD springs, I use a 5/8" - 18 NF bolt to make the adjuster.... If the bolt is large enough, you can even drill it out to allow the (longer) spring to fit up inside the adjusting bolt.... Let's say a 1" long 7/16" bolt with a 5/16" (11/32") hole that is 7/8" deep for the spring to fit inside for Disco (or QB) springs....

Bob

[rsterne]

Here is a general arrangement for the Stopped Spring Guide, for those who may be having trouble seeing how it is built....



The black rod is the spring guide, I make it from the appropriate size drill rod, and the spring seat on the right from a nut, threaded on, peened in place with green Loctite and then machined to shape and the same OD as the spring.... It sits in the end of the hammer, with a small gap.... The green part is the adjusting nut to set the gap between the end of the guide and the inside of the hammer, and acts as a velocity adjuster.... I make it from a fine thread bolt, and you will need to prevent it from self-adjusting, either with a locknut, or a plastic plug pushed against the side with a setscrew, as a brake.... It is threaded into the purple part, which is the rear end cap for the tube, tapped to accept the bolt.... The blue is a 90D O-ring that fits the guide.... The red is a nut, threaded onto the end of the spring guide, and can either be a NyLoc, two nuts locked together, or tightened against a shoulder on the guide (if you don't need it adjustable).... It sets the preload on the spring....

You use a longer, lighter spring than normal, with significant preload, perhaps 1/3 of the cocking force.... You want enough preload that with the guide just touching the hammer the gun will shoot the highest velocity you want (or is capable of with the porting and pressure you are using).... It is therefore a good idea to know what the gun can do before you start playing with springs.... When properly set up, with the correct spring and preload, you will be able to adjust the gun over a wide range of velocity by adjusting the gap, up to the point where the end of the guide hits the hammer.... If you reduce the gap to zero or tighter (actual preload on the hammer), the gun will waste a LOT of air for very little increase in velocity, because the preload will prevent the valve from closing quickly, blowing air out the barrel after the pellet has left.... The muzzle report will be a dead giveaway if you do that, it gets MUCH louder if there is no gap....

Bob

[rsterne]

Today I revisited my .30 cal Grizzly, which is the first gun I installed an SSG into, last summer.... The gun has a 22 CI 3000 psi tank and is regulated at 2200 psi.... I went over my records and found that I had tried five different hammer spring setups in the gun.... The first setup was a 3" long x 0.051" wire spring (15 lb/in), and by the time I had it tuned for the power I wanted the preload was about 0.3", and the cocking effort was about 18 lbs.....  I was getting about 16 shots per fil, with the efficiency teasingly close to 1.0 FPE/CI, which wasn't bad, but I wanted better.... I changed to a 2.5" long x 0.055" wire spring (24 lb/in) with 0.18" of negative preload (gap), and the gun was very hard to cock, especially right at the end of the stroke where it peaked at over 20 lbs.... The gun still had some obvious hammer bounce, even with the short stiff spring rattling around loose when uncocked, and it was so easy to NOT pull the bolt handle back all the way, I was getting many double feeds from the MRod magazine because I didn't quite get it cocked.... I got a maximum of 18 shots per fill.... I then tried a 3" long x 0.047" wire spring (11 lb/in) with lots of preload, and while the gun was much nicer to cock, with less than 14 lbs. of force required, and still gave me the performance I was after, the hammer bounce was horrific, and the efficiency was terrible to match.... It was down to about 12 shots (less than 2 magazines)....

I then made the first SSG, using that same spring, and I couldn't get enough power, so I increased it to a 3" long spring with 0.049" wire (13 lb/in) with 0.55" of preload (7 lbs.) and a gap of 0.12" between the guide and hammer.... That resulted in a maximum cocking force of less than 18 lbs. (the way I started), but it felt MUCH lighter and smoother because it started at 7 lbs.... I never again had a problem with incomplete cocking or the MRod magazine feeding two pellets as a result.... If I reduce the gap to minimum, the gun will reach 1000 fps with the 44.8 gr. JSB pellets, and I am running it 2 turns out from there, where it shoots 967 fps average (93 FPE).... I get 16 shots down to 2200 psi (50 psi per shot) within a 1% ES, and I can shoot a total of 3 mags (21 shots) before the velocity falls to 952 fps (2%ES), at which point the pressure is down to 1920 psi.... That works out to an efficiency of 1.19 FPE/CI, which I think is pretty good at that power level.... My original goal was 2 magazines on a fill.... I got 3.... Here is how the SSG all started....



Bob

[Motorhead]

Lol Bob .... as did I work with my .177 Field target prepped M-rod.

Rifle prior to todays fiddling was working just great delivering @ 82 shots under regulation with 10.3 JSB's at 910 fps.
Hammer weight was a mere 14 grams utilizing the OEM 6# spring with @ 2 1/4 turns preload .... Past shot stings showed efficiency in the 1.40 range.

But hey, ya never know if more there unless you go for it .... right

So right away found out like I had with the .22 M-rod that these SUPER LIGHT hammers don't make the power with the SSG system using the same 6# spring preloaded to the max.  Add some hammer weight and they do !!  ( The .22 had a 20 gram and require 28 grams.  The .177 shared here today had 14 gram and needed 24 grams )  while these hammers weight are ridiculously light by common practice standards, they work so they stay 

Ok TODAYS parts built similar to other rifle using a SS 8-32 screw, tho this time screw head is a lot smaller and has a low friction nylon sleeve down shank.  ( Was there so left it on )  Hat made like the last one done for the .22 using the same wedge undercut to hang onto an o-ring with @.020" compression to bottom out yield. Length for preload and a barrel shape also done for minimal drag.  Head of screw & o-ring pocket into a counterbore to clean up the look.

Parts used like this ...


Assembled like this ...










So with some preload fiddling was able to get the 10.3's back at 910 fps using the OEM 6# spring, tho more hammer weight.
QUIET !!! is an understatement ... think a mouse fart makes more racket !!  JUST WOW

Loaded up my 8 magazines and went outside blasting away till empty ... HUH, still got air left with gauge still setting at set point pressure, so load up 2 more mags shooting 1 making 90 shots and gauge still not moved, start shooting the 10th mag while watching gauge for movement ... 97th shot detect maybe a drop & take the last 3 over the chrony ... yes it was off regulation yet velocity was still 905 to 895 on the last 3 shots.

Into Lloyds efficiency calculator to crunch the numbers ....    avg FPE/cuin per shot 1.73 
( 3k fill, 1.7 set point, 190cc tank, 10.3 g, 95 shots, 910 fps )

Bob ... we have a winner design going on here ... Wow hardly seems sufficient.

Scott

[rsterne]

Hey, Scott, that's pretty KEWL !!!.... Congratulations.... I'm glad to help, and delighted that you have confirmed my findings.... I'm sure you will turn this idea into a bunch of happy customers with a drop-in (or at least tuner installed) setup.... and good on ya! for that !!!.... Advancing the sport is what it's all about for me.... and it's not often you can lay claim to (dare I say it?) a breakthrough.... I'm just having a blast retrofitting my PCPs to see what gains I can make.... 

Bob

[Motorhead]

I'm just having a blast retrofitting my PCPs to see what gains I can make.... 

Bob

Indeed ... sadly for some of my personal guns having vertical thumb rests right behind main tube this mod is not going to make sense.
I am however excited to see what can be done with the BAM 50 .25 cal conversion however.

Scott

[Rallyshark]

Bob,
When you get around to retrofitting your AT-44, please do post!  I have ideas, but I don't have the spare parts and machining equipment around, so I don't want to start "chopping up" the only working parts I have just yet.  I've now managed to get my .22 AT-44 touching the 55fpe mark, but it is an air hog doing it.  Needless to say, if I could figure out a solution like the SSG that will work with the hammer and spring set up on it, that would be awesome.  Given that the spring is basically hanging out in the hammer in there, I'm not sure on the best way to make that happen.  You guys are way more likely to succeed than I

[rsterne]

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

[Motorhead]

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

[Tomg]

Is the At-44 worse than the disco?

[Tomg]

One of the upsides with the SSG is you can "buy" length in the rear cap for the mechanics of it.

[rsterne]

To tell you the truth, it's been so long since I had mine apart I can't remember the details.... It does use a fairly small OD spring, but that makes it stiff (high rate).... Lots of room for a long spring if you take out the spacer and shorten the front spring adjusting screw inside the hammer.... I don't know what would be involved in attaching it inside the tube and moving the adjustments to the back, assuming there is room in there.... At some point I may find out, if I run out of other projects.... *LOL*....

Bob

[lloyd-ss]

You guys are all a bad influence! Instead of doing what I was supposed to be doing today I was fiddling with Bob's new SSG device.
First, gotta say, Bob and Scott, you are both very sick and apparently cannot be stopped.  Lucky for the GTA, ha, ha.  It is amazing how quickly great work can get done when the OCD kicks in. 

So I had to fiddle with the cocking rod version of the SSG to fit in a Disco tube. Darn if it didn't work!  It needs some refinement, but it isn't too far off.

Here are the parts and pieces.  The spring guide is a piece of 1/4 O.D. x .029 wall SS tubing, threaded 1/4-28 at each end.  The makeshift cocking rod is a piece of 3/16, stiff 17-4Ph SS rod that threads down inside the hammer.  I had to heat it to bend it. The adjuster with the 1/2-20 male thread has a stepped hole thru it for the spring guide and the cocking rod.  There is a partition inside of it that retains the spring.  The partition is closer to one end than the other so that it can reversed if you need to get within a different adjustment range for heavier or lighter springs.  The jam nuts for the spring guide are actually 8-32 nuts that I tapped out to 1/4-28 so that they would fit down inside the 1/2-20 adjuster.



This picture shows how the spring guide and its damper and jam nuts get swallowed up inside the 1/2-20 adjuster.



Here is the total assembly ready to be fitted into the gun.  The cocking rod is bent like that to give plenty of clearance for the particular thumb hole stock this is going into.  At this time, the spring preload is already set, and can't really be changed once installed in the gun.  However, the hammer rebound clearance does get adjusted after the installation is made.


This cocking rod version is only needed if you want to use a heavy spring to get power.  I think this is the same spring Bob mentioned earlier: .051 wire x 3" long x .360 dia x 25 coils.
Progress usually takes time!
Lloyd

[pllagunos]

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

[lloyd-ss]

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

[Rocker1]

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

[Rivers3Plinker]

Lol Bob .... as did I work with my .177 Field target prepped M-rod.

Rifle prior to todays fiddling was working just great delivering @ 82 shots under regulation with 10.3 JSB's at 910 fps.
Hammer weight was a mere 14 grams utilizing the OEM 6# spring with @ 2 1/4 turns preload .... Past shot stings showed efficiency in the 1.40 range.

But hey, ya never know if more there unless you go for it .... right

So right away found out like I had with the .22 M-rod that these SUPER LIGHT hammers don't make the power with the SSG system using the same 6# spring preloaded to the max.  Add some hammer weight and they do !!  ( The .22 had a 20 gram and require 28 grams.  The .177 shared here today had 14 gram and needed 24 grams )  while these hammers weight are ridiculously light by common practice standards, they work so they stay 

Ok TODAYS parts built similar to other rifle using a SS 8-32 screw, tho this time screw head is a lot smaller and has a low friction nylon sleeve down shank.  ( Was there so left it on )  Hat made like the last one done for the .22 using the same wedge undercut to hang onto an o-ring with @.020" compression to bottom out yield. Length for preload and a barrel shape also done for minimal drag.  Head of screw & o-ring pocket into a counterbore to clean up the look.

So with some preload fiddling was able to get the 10.3's back at 910 fps using the OEM 6# spring, tho more hammer weight.
QUIET !!! is an understatement ... think a mouse fart makes more racket !!  JUST WOW

Loaded up my 8 magazines and went outside blasting away till empty ... HUH, still got air left with gauge still setting at set point pressure, so load up 2 more mags shooting 1 making 90 shots and gauge still not moved, start shooting the 10th mag while watching gauge for movement ... 97th shot detect maybe a drop & take the last 3 over the chrony ... yes it was off regulation yet velocity was still 905 to 895 on the last 3 shots.

Into Lloyds efficiency calculator to crunch the numbers ....    avg FPE/cuin per shot 1.73 
( 3k fill, 1.7 set point, 190cc tank, 10.3 g, 95 shots, 910 fps )

Bob ... we have a winner design going on here ... Wow hardly seems sufficient.

Scott

NICE work Scott. I really like the craftsmanship and obviously the results.

I am working on building one of these and wondered if you guys had some advice on a couple things.
This is going into a Disco using a Prod hammer which is already relieved and working in the gun.

Parts thus far:

• 3/8-24 Banjo bolt drilled out to 11/64 (.203 )
• 5mm machined steel rod ( taken from a piece of imported office equipment = .196)
• 10-24 stainless nuts ( have to source yet )
• Prod rear cap ( already 3/8-24 threaded internally )

Plan is to fully thread the Prod cap from the inside out using a tap. Conveniently the spring guide that comes with the cap is already this thread so I just need to finish it right out the back end. I've already drilled and tapped holes for the cap for use in the disco tube BTW.

Question:
I see Bob used a 2200 spring for Disco application. What gauge wire and length is that spring? How strong is it?
I have 1322 springs. Would the 1322 work or do you suggest getting a 2200 spring from Crosman or something else?

The 5mm rod in the 13/64 hole seems like a nice, tight, arrangement but I'm debating getting piece of 7075 aluminum rod 5mm instead to reduce mass.
The 5mm is only slightly thicker than the 3/16 and it's only a 3" section so maybe no worries.
Any thoughts on that idea? I'm thinking a lighter spring might be possible with the lighter rod.
I suspect all this is a matter of try it and see but wanted some feedback from yous guys.

Thanks!