A New Method for Increasing the Efficiency of a PCP

[rsterne]

Today I pulled apart my 2560 and fitted the SSG system to that.... Here is a photo of the gun before the SSG was fitted....



It is a twin to the 2260 I did earlier, except uses a 17 CI tank regulated at 1800 psi instead of a 13 CI regulated at 1600.... This allowed it to also get just over 4 magazines per fill (they are 8 shot mags) shooting 25.4 gr JSB Kings at an average of 949 fps with an ES of 9 and an efficiency of 0.96 FPE/CI for 35 shots.... The gun used a QB spring with a small amount of preload, and if turned up to 960 fps had audible hammer bounce and a decrease in shot count....

The SSG is very similar to the one on the 2260, with a 7/32" spring guide, but longer to accommodate the QB spring, so it projects further from the back of the main tube, just like the previous RVA does in the photo above.... This gun, even in the previous version (with the guide acting as a cocking indicator), requires you to lay your thumb along the side of the stock instead of wrapping it over the wrist, where it would be touched by the end of the guide when cocked.... It took a bit of playing on this gun to find the correct adjustments, but it was worth it.... I was rewarded with 50% more shots at slightly higher velocity.... I can now get 7 magazines (56 shots) averaging 960 fps (52 FPE) with the Kings, ending at 1400 psi with a 2% ES, with the first 52 shots within under a 1% ES (9 fps) ending at 1500 psi, which works out to 1.48 FPE/CI, over a 50% improvement.... I have gone from 4 solid magazine per fill to 6, without having to be at all concerned about the velocity dropping off, even with a 2900 psi fill, which is what I get with my Pony tank in the field.... The gun uses only 28 psi per 52 FPE shot....

Once again, I am astonished at the increase in shot count when operating on the knee of the curve by using the SSG.... As long as it has a gap to the hammer (this gun had 1 turn = 0.042"), the report is much quieter, just a clean SNAP, with no telltale BUURRRPPPP of hammer bounce.... Both of my Varmint rifles now have a 50% higher shot count than last year....

Bob

[rsterne]

I installed an SSG in my Grouse Gun today.... 2260 PCP Carbine with a 14" barrel and a stock Disco valve and hammer spring.... I used a 2200 spring with 0.90" of preload, which puts it very close to coil bind when cocked....

Previously I got 16 shots with a 2% ES, and 20 shots within 4%, averaging 20 FPE (705 fps with JSB 18.1 gr. heavies), with an efficiency of 1.15 FPE/CI

Now I get 20 shots with a 2% ES and 24 shots with 4%, averaging 21 FPE (722 fps), with an efficiency of 1.50 FPE/CI, an improvement of 30%....

It doesn't seem to matter if the PCP is regulated or not, the SSG can provide big gains in efficiency....

Bob

[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 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....

Bob

[rsterne]

I rebuilt the first gun (2260/Disco) I converted to the SSG today, using the last drawing in the post above.... It uses a much shorter spring guide that moves with the hammer, so the energy is not wasted.... Here are the two types.... I stole the spring from the top one for the new one, on the bottom....



The top one has a long guide that stops when the rear nuts hit the gap adjusting bolt.... The bottom one has a sliding aluminum collar that pushes against the end of the gap adjusting bolt when you cock the gun.... and the stop nut slides back inside the adjusting bolt.... When you fire, the guide accelerates with the hammer, and just before it hits the valve, the stop nut hits the collar and carries the collar with it.... All the moving parts provide their energy to the valve.... The gap adjusting nut must be larger in diameter to allow the stop nut to pass through the center when the gun is cocked.... The collar is centered in the front of the end plug, which keeps everything aligned.... You can see how much shorter the new setup is than the original, and when cocked, the stop nut stays inside the gap adjusting bolt, as in the photo below....



The photo above is with the gun cocked.... Compare that with the photo below of the original SSG setup, also with the gun cocked....



There is no longer a pinch point to worry about, and it looks MUCH nicer and more compact....

How does it work?.... FABULOUS !!!.... When I first assembled it, I used 0.1" less preload than I did in the original version, because I expected a stronger hammer strike and I didn't want to go past where I wanted to end up.... Well, it turned out I should have reduced the preload by 0.2", because I had more velocity than I wanted from the heavier hammer strike.... When I cranked it up (with no gap) it was well over 1000 fps with Kings, and I just happened to have some of the new 34 gr. King Heavies here, so I tried them.... With a minimum gap I was in the mid 800s, which was 55 FPE, compared to the best I could do with the old SSG with the Kings of 50 FPE.... So, I pulled it apart, increased the preload to maximum with the 2200 spring, and was rewarded with even more velocity.... By maxing out the spring to coil bind (preload, no gap), I hit 948 fps (68 FPE), which is harder than this gun has ever shot before.... Once I backed it out to get a tiny gap, it was shooting right at about 900 (62 FPE), but it was using a lot of air, so I backed it out another turn, and settled for a peak velocity of 880 fps with a 5-shot string from 2000 psi down to 1300.... The average was 866 fps (57 FPE), at an efficiency of 1.30 FPE/CI.... which is pretty astounding for a mildly modded Disco with the small tube from a 2260....

I really like this version of the SSG, particularly for guns where you need lots of hammer strike to get the dwell for high power with heavy pellets.... It still has the advantage of eliminating hammer bounce, but it doesn't waste the energy the spring puts into the guide, instead it uses the weight of the guide to increase hammer strike and dwell.... In addition, it is much more compact, and the guide can be hidden inside the adjuster, providing the hammer stroke isn't too long (this gun is 0.65").... All in all, I think it's a significant improvement over the original.... particularly for higher powered PCPs....

Bob