Canadian Airgun Forum

Today I installed an SSG in my 2260 reversed tank HPA.... It previously got 43 shots with JSB 18.1 gr., from 3000 psi down to 1400 averaging 958 fps (37 FPE).... It had a 1.75" x 0.040" wire hammer spring (14 lb/in) and took about 11 lbs. of effort to cock.... This is the gun I'm talking about....



I made a Stopped Spring Guide to carry a 2.00" long 0.040" wire spring (12 lb/in) with about 0.45" of preload (~ 5.5 lbs), and played around with the gap to get the same velocity I had previously.... The gap ended up about 0.040", and the cocking effort was about 12.5 lbs.... The ideal spring would have been slightly longer with a 10 lb/in. rate, but I didn't have one, and as it turned out it doesn't matter.... Even though the maximum cocking force is slightly greater, because it starts out at 5 lbs. instead of less than 2 lbs., it feels smoother and you don't have that sudden increase in force right at the end, that sometimes causes you to not quite cock the gun, which with the MRod magazine causes a double feed.... In all the shots fired during testing (over 200) I never had a mis-feed.... Here is what the old RVA and the new SSG look like....



The old RVA used a floating spring guide that was captive between the spring and the hammer and extended through the adjusting bolt as a cocking indicator.... The 10-32 nut on the back of the new SSG is against a shoulder on the 7/32" guide, so I didn't need a 2nd nut to lock it, I just snugged it up with Loctite.... so the total length when cocked is nearly the same.... During testing springs I noticed that the pressure guage wasn't dropping as fast as before, so I was pretty anxious to check the shot count and efficiency.... Using the same pressure range as before (3000 psi down to 1400) I got 60 shots (instead of 43) averaging 966 fps (8 fps faster) with an ES of 10 over the string (12 previously).... The shot count, and the efficiency, increased 40%, to 1.49 FPE/CI (from 1.07).... I was absolutely SHOCKED and delighted by this result.... There is no question that the SSG can make a huge difference, particularly in a gun where you are pushing the power....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Good results Bob. Is there a chance that if the traveling parts of the SSG were made of Ti that it would do even a bit better? Maybe just in big bore applications? Regards, Tom

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tkerrigan Jefferson, Oregon

You are thinking to save weight and the associated wasted spring energy?.... I suppose so, if it becomes an issue.... I will know better once I get my Monocoque PCP finished, as the guide is 1/4" diameter and 5" long.... 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

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

hi Bob...quick questions. I am going to do this on my disco, and already had it drilled for 3/8 bolt so I can remove spring in the fly.
How long is the bolt that you used for this mod? I tried to drill the bolt but it is not perfect so going to get the guy at work to drill for me tomorrow (I need a lathe). I know 3/16 is .1875, and you look to have lubed it (moly?). What size did you drill hole through bolt for clearance?
I found a piece 3/16 rod exactly 3 inch long by fluke in my pile so going to thread that tonight. Is that still the length needed? I guess the front end is just threaded enough to get it on and then peened over. I might even weld it lightly and then grind it smooth. Is there an difference if that end is ground flat or domed?
Thanks in advance.

The length will depend on the spring you use.... If you use the stock Disco spring, you will increase the cocking effort because of the preload.... and you may run into coil bind at the other end.... That is why I suggest a longer lighter spring.... For a 3/16" guide, I used the next size up numbered drill (#11), you might have to go to a #10 (0.1935").... The bolt I would use is a 1" long 3/8"-24 NF hex head bolt, and I thinned the head a bit, though not necessary to do that.... You won't be able to drill the center out big enough for the spring as on the drawing, so you may end up shortening the bolt if you need to.... You can thread the ends of the guide 10-32, no need to even turn it down first.... I like to make the front end domed, I think it centers well in the end of the drilled hole in the hammer (which has a typical pointed bottom from a drill)....

At this point in time I haven't done a "stock" Disco, so I can't make a spring or length recommendations.... you will have to experiment to find what works for you.... It MAY be possible to use a 13XX spring, or possibly two pieces of 13XX spring to make it longer.... Make sure you close the coils on the ends so that it can't wind into itself....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

That's the info I need. Thanks Bob. I think I have the .040 spring snipped to 1.75 on my .22 disco , but I have a few that somebody from GTA sent me and I think one is 2"+ and .037 or .035 so I will check them, otherwise I will order one.

I replaced the 1.75" x 0.040" with a 2200 spring.... worked OK, but pretty much on the limit.... If you were using the 1.75" x 0.040" with a lot of preload the 2200 won't be strong enough.... Something like 2.25" x 0.037" should be good....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Just checked and all my springs are .040 and longest 2" so going to have to source one. I wish I could find a local source for them (southern Ontario, Niagara Region). I have a good nut and bolt place but not springs.

try trakar springs.

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Don't take life too serious... It's not like you're gonna make it out alive.

Thanks AFA. Crosman shipping from Quebec just takes too long.

Hi Bob...almost done. I am going to tack the front end nut with welder after work and grind/sand smooth and chuck in drillpress and file down OD tonight and hopefully try if I have enough daylight left.
Quick question so I don't have to keep taking out and trying to fit in hammer...what is the OD of that front nut that goes into hammer?
Below is where I was at last night. I put it together and had too much load on the spring so I cut 1/4" off the bolt and thinned out the head a bit after that picture. I used a .032 1.5" spring that I had and added a piece of .040 spring .75 long to make the overall 2.25" until I can get one. Might not work but that is all I had.

The front nut should be the same diameter as the OD of the spring, there is no reason for it to be larger, because the (round) spring wire contacts it slightly in from the OD anyway....

For those of you trying to wrap your brain around what is happening to the efficiency here, this drawing may help.... It is "generic", the numbers are ficticious (but representative), the purpose of the graph is to give you a visual comparision of how the various types of hammer spring setup affect the efficiency curves.... and then hopefully explain why they are the shape they are....



With a conventional, preloaded hammer spring, the spring is in contact with the hammer all the time, even when it is opening the valve.... It actually helps the hammer open the valve, and slows the poppet on the return trip.... In a stock Disco, for example there is about 1/4" of preload and the valve only opens 1/16-1/8".... As you increase the preload, the hammer spring holds the valve open longer and longer, and eventually you get to the point where the valve is still open after the pellet leaves the barrel, and the velocity no longer increases.... This is shown by the plateau in the velocity curve on the above graph.... As you continue to add preload, you continue to waste more and more air however.... The efficiency curve is typically a shallow "S" curve as shown....

If you use a shorter, stiffer spring, if it is adjusted for a gap between the spring and the hammer (let's say zero preload occurs at -3 Turns out from coil bind), from there and out, the gap means that the hammer spring is no longer pushing on the valve stem directly, it has "launched" the hammer, which then does all the work.... It is proven that this setup generally has less air-wasting hammer bounce, and better efficiency, providing there actually IS a gap.... If you increase the preload to where there is no gap, you can waste even more air than with a weaker spring, because the higher force can retard the valve closing even more.... However, for the way you would normally tune a gun, on the "knee" of the velocity curve, you tend to get better efficiency.... This setup, however, for a given average spring force, will be harder to cock, particularly at the end of the cocking stroke.... and it is still possible to get some hammer bounce, because the spring, when the hammer first strikes it, has by definition zero preload, and will give easily, storing some energy to be returned as hammer bounce....

With the SSG, when properly adjusted to have a gap between the end of the spring guide and the hammer when uncocked, the spring again does not push on the hammer while it is in contact with the valve, the hammer does all the work.... If you adjust the gap down to nothing, and then start adding preload, then there is a very large spring force against the hammer while it is opening the valve, which holds the valve open, wasting air.... The point where the gap reaches zero would be at -3 Turns out on the graph.... The velocity at which this occurs (the knee of the velocity curve) will depend on the amount of preload on the spring, and the average spring force available to launch the hammer.... You might gain a few fps by adding preload, but the amount of air wasted will NOT be worth it.... On the other hand, once there is a gap, the efficiency is very good, because the large amount of preload prevents the hammer, when it is thrown back by the valve on closing, from storing energy in the hammer spring which is then returned, causing air-wasting hammer bounce.... The gap acts very much like an "of-off" switch for the efficiency.... With a conventional setup, there is a slope to the efficiency, increasing as you decrease preload.... while with the SSG, it is pretty much either "efficient" (with a gap), or "inefficient" (without one)....

I hope this helps you understand why I'm so excited by this development....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Hello Bob. Nice setup, but it looks a bit familiar. I posted a similar setup a while back which I called a slingshot hammer, but was wrong with the name. Yours is much better with the steel pin to further stop the hammer bounce. Great job.
Post subject: Re: Hipac Owners
PostPosted: Wed May 07, 2014 10:24 pm
The slingshot hammer , as I call it, is not really a slingshot hammer. Merely a short heavy hammer spring so that the hammer does not rest on the valve stem, no pre load, when the hammer flies foreward it opens the valve but has no hammer bounce thus saving air. The problem is getting just the right spring.

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If I had only one wish, it would be to be able to "unsay" things.

Joe, the idea of using a short, stiff hammer spring has been around for a long time, pioneered by Lloyd Sikes, who first noticed that it could result in an increase in efficiency due to reduced hammer bounce.... It does, however, make for the highest cocking effort of any of the systems, for a given hammer enerfy.... Daystate have a patented "Slingshot Hammer" which is a two piece affair where the outer part of the hammer stops by hitting the valve body, while the inner part continues to open the valve....

The short, stiff spring like you used, can indeed save air, but as there is no preload against it, when the hammer is fired back by the valve it can still store energy and cause hammer bounce and waste air.... That is exactly what was going on in my Grizzly, which prompted me to come up with the idea of using a spring guide with a stop on it to allow you to preload the hammer spring while not allow it to touch the valve.... It is that preload that prevents the hammer from bouncing and wasting air....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

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

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!