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

[oldpro]

bnowlin I didnt put the adjustable spring poppit in front of the NBH to prevent bounce thats what the shoe on the hammer does I put it there to prevent over dwelling the valve at lower pressures thus extending the shot curve and not creating burping at lower pressures. It worked fantastic but trying to explain to customers how to set the curve and dwell and poppit distance was overwhelming so I deleted it unfortunatly.

[bnowlin]

Yall make my head hurt anyway, but it was just a thought LOL.  Bob makes a lot of sense.  Like the TV commercial "Grandpa how do you know so much"?  I still like all your mods Travis.  BTW Bob thanks for explaining.  You to young-en.
Bob

[wll2506]

I'm ordering a couple of parts for my Disco this am.

Your idea is very, very simple to do and sounds like it makes a huge difference in the guns dynamics (more shots, quieter, more consistency) What i like is all parts are at your local hardwars store and more heavy duty machining or expensive equipment is required to do it !

I'm very much looking forward to trying this ... does this in effect do away with the RVA ?


wll

[wll2506]

Bob,

Using a stock Disco hammer spring and clipping a couple of coils off and then doing your SSG, would that soften up the spring a bit where someone would not need to go and buy or find another lighter spring ? Just curious !

Also, it looks like this modification will not work on the QB series of guns ... gosh darn !

wll

[Gerard]

If you did the reversed cocking mod, cock on open, it might allow for an SSG, no? Of course that could be nonsense, only guessing, as I've not done that change on mine. I actually like the stock setup for the bolt, and have resolved hammer bounce with an O-ring buffer ahead of the hammer combined with a little steel friction denouncer, so won't worry about an SSG for my QB78.

[rsterne]

wll.... clipping coils off a spring actually INCREASES the spring rate (makes the spring stiffer).... but it reduces the preload in a given amount of space (which is why it detunes a non-adjustable gun).... You want the opposite effect to use an SSG to the best advantage, a longer, softer spring with lots of preload....

I did a QB earlier in this thread, but it was cock-on-open....

Bob

[Motorhead]

First FAILURE to get a working or more efficient SSG    .... Not for reasons of the actual devise, but one where no gain was found using it.

BAM 50 regulated conversion gun where rifle was set up using a quite light 30 gram hammer, relatively long @ 15# spring.  Rifle was launching 25.4's @ 900 fps while giving near 1.40 efficiency numbers. 

Made up my typical design SSG and no mater how much spring energy added could not get the power back.
* Obviously a hammer weight issue, So ... tossed in a modified factory hammer of @ 90 grams and tried again.
Yea it worked and made the power, but air use was no better and gun got louder too    Longer dwell from the greater hammer weight. More noise = more air use, so we actually went backwards.

So took the set up back to where it was and calling it good as it was.

Have no doubt this particular rifle as set up could be balanced with some hammer weight in-between the 30/90 gram weights played with.
* Whats interesting and being a first where a REALLY LIGHT HAMMER set up conventionally worked better than the HEAVY factory hammer and an SSG devise.  It leaves me to ponder that hammer weight still plays a role here in controlling dwell independent of hammer bounce issues we have been focused on 

[rsterne]

If you aren't getting any hammer bounce that is wasting air with a given tune, then the SSG cannot improve on the situation.... That seems obvious, and is proof that you had already done your homework.... I had a failure in getting back to where I was for power in my Hatsan, likely due to the room available because of the rear block, and the fact I could not move the rear spring seat further back because of the trigger assembly being in the way.... I think we have to accept the fact that some guns just will not benefit from the SSG (unless some other creative work-around is found).... while others benefit greatly....

Bob

[shorty]

The last 2 posts (motorhead and Bobs) is very interesting to me.

For me, using a short stiff spring I can get a great efficiency. For Scott, the light weight hammer gets his great efficiency.And Bob mentioning that if the system is already efficient the SSG may not improve it.

What's going through my head now is, how efficient can we make our guns.

Is there a calculation (or example) that tells us what the max efficiency can possibly be with lift and dwell. I already know and proved on my gun that fps was not only dependent of lift but dwell affected fps just the same by using a steel stop for lift control.

I would like to leave bounce out because bounce mostly occurs at very low pressures .

[RONIN001]

I think Electronics will control the future of ultra efficient air rifles but then what do I know after reading some of Bobs post my brain was scrambled.  lol 

[Gerard]

At the bottom of Lloyd Sikes' PCP efficiency calculator page he's got a chart indicating roughly the potential efficiencies for Low, Moderate, High, and Maximum Power PCPs. In that order he lists ranges of    1.4 to 2.0, 1.0 to 1.4, 0.7 to 1.0, and 0.7 or less. So it seems he's saying maximum efficiency is directly tied to output power, with more power equating to lower efficiency. In the low power range one example is my Pardini K12, from which I get over 100 shots per fill though it's just a tiny air pistol cylinder, averaging a bit under 5fpe. I don't know the internal volume of the cylinder so can't calculate efficiency, but there's really not a lot of waste going on. If I crank up the hammer spring I can get up to about 7.5fpe max, but it's loud and the shot count drops to half.

The best efficiency I've managed with an airgun is about 1.65FPE/CI, using a short, moderately firm spring on an RVA and a lightened striker, this on a relatively low-ish power Crosman carbine. Adding an SSG and playing with various spring strengths and lengths has so far netted me shorter strings and poorer efficiency. No doubt I'm doing something wrong, but on the other hand the simpler RVA setup with the short spring was a very thoroughly worked out tune, something I spent a lot of time refining.

On a different Crosman, a 2260 to which I added an SSG last night and finished adjusting this morning, I've been able to take it from 1.32FPE/CI with a similar shorter spring and RVA with lightened hammer up to 1.53FPE/CI at about 18.8fpe, using moderately strong springs with a lot of preload. Shot count increased with the 2260. I expect some different spring gauges will help in fine-tuning the first airgun so as to bring me back up to a higher shot count and efficiency in that lower powered setup.

If you're after raw power from a big bore I think just dumping as much as you can into the pellet/bullet is going to net the desired result, but if you can manage to live with dialing the power back 20% or a bit more an SSG will probably be useful in increasing shot count and consistency. Specific numbers... I have no idea, and I'm unlikely to do anything with anything larger than .22" anyway, just don't have the need. Same for power levels as more than about 20fpe is more power than I'll ever want for airgunning. In some of Bob's older posts in castboolits and other places he indicated that dialing back in velocity a bit enabled increases in power for moderately high-powered applications something like jumps from 1.05FPE/CI to 1.20FPE/CI. The SSG might well shift both those numbers upwards on some rifles.

[cilami]

On a different Crosman, a 2260 to which I added an SSG last night and finished adjusting this morning, I've been able to take it from 1.32FPE/CI with a similar shorter spring and RVA with lightened hammer up to 1.53FPE/CI at about 18.8fpe, using moderately strong springs with a lot of preload.

Gerard,

Could you tell us the volume of your 2260 reservoir and the number of shots at 18.8 fpe you are getting after installing the SSG? I am going to try the SSG on my Prod and some pics or details of your setup would be very helpful, if possible. 

[Gerard]

Sure. It's actually averaging 18.88fpe over 21 shots using 14.39gr JSB Express pellets. Volume of the 2260 reservoir after subtracting the long front fill plug (foster type, metal filter at inner end, two O-rings) and the aluminum gauge block, is 65cc remaining ahead of the modified Disco valve. Pressure dropping from 1500psi to 600psi. My results with the SSG were all over the place, initially giving only five reasonably consistent shots from 1,000psi. I could attain as higj a figure as 896fps with no SSG gap. More pressure was provong difficult  as velocity was often dipping below 500fps. A lot of trial and error sorted things out. The correct settings had it climbing to 21 shots. There is now about 0.03" gap. Initial preloaded spring 'weight' is about 6lbs. Bolt draw climbs to around 18bs at the instant before the sear catches. I might be able to use longer springs with thinner wire with a longer guide rod and rear cap,... but I like the steel cap I have and don't mind the hard bolt handle pull. Softer springs with this guide rod length just didn't work at all. Velocities were between 200 and 450fps with the longest 0.8mm wire spring I could cram in without coil bind preventing cocking.

[cilami]

Thanks Gerard! That should save me some time and pellets...

[Gerard]

Yeah... pellets... dangit. Must have put 700 of those little JSB jewels over the F1 in the past week trying to wrestle two SSGs into shape. But it's for a good cause if we all share. Just wish JSB pellets weren't fast approaching .22lr in cost!

[rsterne]

Here are all the major variations of the SSG that have been invented so far.... They all share two common traits.... there is preload in the spring, but the spring does not push on the hammer at rest when uncocked.... These two features combine to prevent hammer bounce.... The concept first discussed was to use a Gas Ram to achieve this, but unavailablitly of a suitable unit caused me to simulate the way it worked by using a spring on a guide with a stop to create the preload and a gap to the hammer.... Here are the various configurations suggested to date, some tried and some not.... All these drawings share the same features and were drawn to the same scale, although they may have changed slightly by the time they got uploaded....

1. They have the preloaded spring 10 units long.  Spring and guide is shown in black.
2. They have a hammer stroke of 7 units, with enough room for that to occur everywhere.
3. They have an adjuster (shown in red) for the gap between the hammer guide and hammer, which also changes the distance the spring compresses when cocked.
4. The green feature is the end cap, all end caps and gap adjusters are drawn the same size.
5. The hammer is shown in purple, and is longer for the ones that require a deep hole in it.
6. If a sliding collar is required on the guide, it is shown in blue.



Gas Ram suggested by stalwart



SSG suggested by rsterne



Above suggested by bstaley.



Above suggested by Gippeto.



Above suggested by I_like_Irons



Above suggested by rsterne



Above suggested by rsterne

It is not the intention here to show every possible variation of materials or construction, but only the major differences in operating methods.... In my original design, the spring is captive in the rear gap adjusting nut, is accelerated by the spring and comes to a halt just before the hammer hits the valve, wasting the energy used to accelerate it.... After my original design, which several people have tried, two variations were proposed in which the guide was fixed at one end.... In Gippeto's version, it was fixed at the back, adjustably, into the gap adjuster in the end cap.... The guide does not move, the spring does its work pushing against a sliding collar which then pushes on the hammer.... The collar stops just before the hammer hits the valve.... No energy is used in accelerating he guide, only the small collar.... but the weight of the guide does not assist the hammer strike.... In a version proposed by I_like_Irons, the guide is fixed in the hammer and travels with it, but maintains preload adjustability where it threads into the hammer.... It also uses a sliding collar on the guide, but at the back, pushing on the gap adjusting nut.... The weight of the guide takes energy to accelerate, but that energy becomes part of the hammer strike....

The two remaining versions I have proposed, to take advantage of the above ideas, but without requiring the guide to be fixed to either part, it remains free-floating, with a gap to the hammer adjustable by the red adjuster.... Both versions require the sliding collar.... In the first version, the guide remains stationary and the collar slides, like in Gippeto's, requiring no energy to accelerate it, but does not contribute any to the hammer strike.... In the second version, the guide travels with the hammer, while the collar stays still, like in I_like_Irons version.... which requires energy to accelerate the guide, but it gives that energy back as part of the hammer strike....

The versions where the guide stays still at the back don't stick out the back of the gun, but require room inside the hammer to accommodate the guide during the cocking stroke, so the hammer has to be deeper than the stroke.... The versions where the guide move with the hammer don't stick out the back as far as my original version, but require that the back end of the guide, including the diameter of the stop nut, be able to clear the inside of the gap adjuster without interference or hanging up.... Each version will have it's own limitations, advantages and disadvantages.... Some will be suitable in some guns and not others, and vice versa....I hope by showing all the versions in one place that might help clarify their similarities and differences....

I apologize for not including bstaley's suggestion, I have now added it, in the order it was suggested.... I simply missed it when doing this compilation.... It uses the guide rod passing through the hammer, with a gap between it and the valve stem.... The hammer must be shortened by the thickness of the stop on the front of the guide.... The gap adjuster still works the same, but against the end of the shaft, and the preload can be set by moving the stop nut on the guide.... The guide is stationary until struck by the hammer, which then must accelerate the mass of it and the spring before striking the valve.... Otherwise, it has all the same features as the others....

Bob

[Motorhead]

Bob,
Very nice consolidation of design ideas.
Sadly few PCP guns have sufficient distance or length from hammer to rear retention cap to utilize many of these designs.
Personally having quite a few PCP's and working on more, ORIGINAL design first proposed appears in my estimation to be the most applicable to the PCP guns many would find them self's modifing for SSG fitment.

Unless something monumental in our collective think tank is being over looked, see a few mainstream manufactures taking notes here and producing similar systems in the foreseeable future.

[rsterne]

Yeah, that's why I wanted to draw all the diagrams with the same criteria for (preloaded) spring length, hammer stroke, and hammer to rear end cap distance.... so we could visualize the pros and cons of the different ideas.... The two designs with the guide remaining stationary at the back require a very deep hole in the hammer (the stroke plus the distance the end of the guide sits inside at rest), so they would require different hammers, I would think.... The two designs where the guide moves with the hammer and supply part of the energy and momentum, both have the same problem at the back, where the stop nut at the back of the guide, which is going to be AT LEAST the OD of the spring (and more if it's actually a nut), has to travel through the gap adjusting bolt, UNLESS there is a ton of room between the hammer and the rear plug....

Having said that, I intend to try the bottom version next, because it is very close to my original design.... All that is different is that sliding collar, and a larger adjusting bolt required so that it can have a larger ID to accommodate the stop nut.... I really like the idea that all the work the spring does gets to smack the hammer, instead of a large percentage of it going to waste.... In addition, the load on the guide stop is tiny, it just has to accelerate the collar at the end of the stroke.... instead of having to stop the mass of the guide and spring.... We can probably do away with the O-ring entirely on the bottom design....

It will indeed be interesting to see over the next few years if any of the manufacturers are paying any attention.... 

Bob

[Motorhead]

Having said that, I intend to try the bottom version next, because it is very close to my original design.... All that is different is that sliding collar, and a larger adjusting bolt required so that it can have a larger ID to accommodate the stop nut.... I really like the idea that all the work the spring does gets to smack the hammer, instead of a large percentage of it going to waste.... In addition, the load on the guide stop is tiny, it just has to accelerate the collar at the end of the stroke.... instead of having to stop the mass of the guide and spring.... We can probably do away with the O-ring entirely on the bottom design....
Bob

If I understand the bottom design ... the Entirety of the spring / rod unit is floating upon strike of valve.  Gap could be Stop rod to hammer or Stop rod to rear cap ?
The WEIGHT of the spring & rod in terms of momentum to valve add to that of hammer, yet due too them floating just prior to impact ... will they contribute to the strike energy or rebound/bounce around absorbing some

Minds pondering that one 

[rkr]

Having said that, I intend to try the bottom version next, because it is very close to my original design.... All that is different is that sliding collar, and a larger adjusting bolt required so that it can have a larger ID to accommodate the stop nut.... I really like the idea that all the work the spring does gets to smack the hammer, instead of a large percentage of it going to waste.... In addition, the load on the guide stop is tiny, it just has to accelerate the collar at the end of the stroke.... instead of having to stop the mass of the guide and spring.... We can probably do away with the O-ring entirely on the bottom design....
Bob

If I understand the bottom design ... the Entirety of the spring / rod unit is floating upon strike of valve.  Gap could be Stop rod to hammer or Stop rod to rear cap ?
The WEIGHT of the spring & rod in terms of momentum to valve add to that of hammer, yet due too them floating just prior to impact ... will they contribute to the strike energy or rebound/bounce around absorbing some

Minds pondering that one 

That's to be tested. As part of the spring is not accelerating or accelerating at lower rate the SSG combo could follow the hammer a millisecond or few milliseconds behind it. If it does then the effect will depend on the timing it strikes the hammer. If it's short enough it will add dwell, if it's longer it will hit the hammer on rebound and kill the bounce.