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

[match]

how about using a multirate spring or 3 springs with the spacer each progressively stiffer?

[rsterne]

how about using a multirate spring or 3 springs with the spacer each progressively stiffer?

What would the benefit be?.... I think it would simply require more length to accommodate the lower rate springs.... I actually tried that today while looking for springs for my Hatsan, and the weaker spring ends up at coil bind before the heavier spring really does much.... so I didn't bother....

Bob

[ajshoots]

I greatly appreciate all the work by Bob and everyone who has added to this thread. I have been following, but haven't had time to test until today. I made a very crude ssg for my wifes .177 marauder. It was getting 50 regulated shots with 10.5gr pellets at 905fps. With my crude ssg and nothing else, it got 90 shots at 909fps. My ES did climb from 16fps to 31fps, but I am sure that I can easily improve the design I used and get the ES back down. It used 1700psi for the 90 shots. Probably not nearly as good as many of you have done, but I am very impressed and thank all of you for the time and dedication in this thread!!

[Rallyshark]

I greatly appreciate all the work by Bob and everyone who has added to this thread. I have been following, but haven't had time to test until today. I made a very crude ssg for my wifes .177 marauder. It was getting 50 regulated shots with 10.5gr pellets at 905fps. With my crude ssg and nothing else, it got 90 shots at 909fps. My ES did climb from 16fps to 31fps, but I am sure that I can easily improve the design I used and get the ES back down. It used 1700psi for the 90 shots. Probably not nearly as good as many of you have done, but I am very impressed and thank all of you for the time and dedication in this thread!!

AJ 90 shots is still pretty darn good I think!  I forgot the formula for efficiency, but that is 1734 total foot lbs total, and I know that is great efficiency.  I'm still waiting patiently for when he nails down his Hatsan, so I can play copy cat  

[rsterne]

You likely have some drag occurring somewhere in the system (possibly the guide in whatever it is sliding through) that is either causing the launch velocity of the hammer to be inconsistent, or on the hammer itself (possibly the spring or guide rubbing inside it), which is causing the inconsistent velocity....

Bob

[I_like_Irons]

I know I'm late to this party, but I have a bit different idea:  Why not turn things around?  Fix the spring guide in the hammer, and let the mass of the spring and guide be part of its mass.  That way, you do not have a loss of hammer energy, and more momentum for a given spring and compression.  You would have a spring that departs from the rear end cap for the clearance. 

I'm also thinking that you could use a cable type retainer inside the spring instead of a guide to control its extended length.  A guide cap on the free end would retain the cable and could be screw adjustable from the access hole in the end cap.

Edit to add a picture for clarity:

Both concepts are in sectional view.

[Rallyshark]

I know I'm late to this party, but I have a bit different idea:  Why not turn things around?  Fix the spring guide in the hammer, and let the mass of the spring and guide be part of its mass.  That way, you do not have a loss of hammer energy, and more momentum for a given spring and compression.  You would have a spring that departs from the rear end cap for the clearance. 

I'm also thinking that you could use a cable type retainer inside the spring instead of a guide to control its extended length.  A guide cap on the free end would retain the cable and could be screw adjustable from the access hole in the end cap.

Thought about this earlier, but I didn't see a cable holding up over repeated shots.  It will stretch, and eventually break I'd think.  Also, that set up as you describe would require pre-load on the valve, which is the opposite of what the SSG does.  It would keep it from over traveling, and may help some, but I don't see a way for it to do what the SSG does.  Theoretically, I guess you could do a cable set up that would work similar the SSG, but you would have to de-couple the hammer from the spring.   Somebody correct me if I'm wrong here, it wouldn't be the first time 

*edit
The last part about the cable spring retainer may work, I missed that the first time I read this, because you're talking about two different things.

[benzy2]

Anyone know the thread size of the spring guide on a Marauder (specifically .177 if it matters)?

[rsterne]

I think the idea with the spring guide mounted on the hammer should work, and as I see it there would be no preload on the valve, because the stop on the guide prevents the spring seat from touching the end cap when uncocked.... It is the exact opposite of the idea proposed by Gippeto, where the guide is fixed to the end cap, and hence takes no energy from the spring.... I'm sure as this idea gets bashed about, there will be even more versions of it.... The original one I proposed does not require a different hammer, although you could certainly change it.... Gippeto, and of course this latest one, both require a different hammer.... All will have advantages and disadvantages, and various degrees of simplicity....

Bob

[I_like_Irons]

Anyone know the thread size of the spring guide on a Marauder (specifically .177 if it matters)?

If you are referring to the tension adjustment screw in the end cap, the Gen 1 is 1/2--20.  It has a spring guide stub and an Allen wrench hole.

[I_like_Irons]

The original one I proposed does not require a different hammer, although you could certainly change it.... Gippeto, and of course this latest one, both require a different hammer.... All will have advantages and disadvantages, and various degrees of simplicity....

Bob

One could use the original hammer with my concept but with replacing the valve striker (hammer length adjuster) with the guide rod/etc.  This would be a rather simple thing to do. 

[rsterne]

I played around with the Hatsan today, and got the SSG working in it.... sort of.... First of all, here are the changes to the gun.... First the stock....



You can see the recess ground in the top of the stock to miss the stop nut on the SSG.... This is a mirror image of the one in the rear plug, posted earlier.... Now the rear plug, with the SSG in place.... The gun is uncocked, all you can see is the stop nut and the O-ring, against the back of the plastic rear plug.... The guide rod passes through the existing hole in the middle of the plug....



You will notice that I also had to grind a recess in the bottom of the safety button to miss the stop nut, as well as the rear plug.... I don't have a photo of the SSG out of the gun at the moment, but here is a view of the top of the tube and you can see the SSG inside.... The spring sits in it's original seat in the front of the rear plug....



It consists of two 1.75" x 0.045" wire springs on a 3/16" guide, with a preload of 1.2" (almost 14 lbs !).... The cocking force peaks at nearly 19 lbs., but of course the side lever makes easy work of that.... Lastly, here is a photo of the gun reassembled, this is the cleanest possible installation, you can't even see the SSG....



When I saw how much preload was on the original tube, I was concerned that I could come up with an SSG that would be able to launch the hammer hard enough to create the 72 FPE the gun was shooting before.... because the original spring preload of 9 turns (nearly 9 lbs.) would have been supplying a lot of the valve dwell.... Well, as it turns out, I was right.... I have only done one trial (and might actually give up on this SSG conversion), the results were a 21 shot string from 180 bar down to 120 bar, with 25.4 gr. JSB Kings from 952-979-941 fps.... That averaged 52.9 FPE, for a total of 1110 FPE from 14 CI x 60 bar = 840 CI of air total, which works out to 1.32 FPE/CI.... The closest comparable string I have with the original hammer spring setup, was with 5 turns of preload, from 171 bar to 120 bar, 16 shots averaging 52.8 FPE at an efficiency of 1.18 FPE/CI.... Both strings had a 4% ES and the same FPE, so they are roughly equivalent.... This means I have gained 31% more shots, at a 12% increase in efficiency.... However, there is no way with these springs in the SSG I will even come close to 72 FPE....

I have the setscrew in the hammer set right to the bottom, and adjusted the gap to a bare minimum (~ 0.020").... There is so much preload on the hammer spring that when cocked it is within about 1/16" of coil bind.... so there is nothing more available without using a stiffer spring.... At this point, I don't think it's worth it.... I will ponder it for a day or two, but this gun is probably going to return to normal.... The one thing I did accomplish, which I never managed before, was over 2 magazines with the JSB Kings at over 950 fps, so it's a decent setup.... just not the 72 FPE monster I know this gun can be....

Bob

[rsterne]

replacing the valve striker (hammer length adjuster) with the guide rod/etc.

Yes, that would work on an MRod or PRod, but not on a hammer that wasn't drilled and tapped down the middle.... and most of them are hardened which would make that extremely difficult.... Still, it looks like a variation that should work....

Bob

[Airsnipe]

I wonder if this could just as easily be accomplished by providing the free space for the hammer to travel independent of hammer spring contact but not preloading the hammer spring? Their are several guns like this that do not burp air behind the shot. I think many FX guns are like this. Just a free floating hammer without the complications of pre-compressing the spring and the extra shock of the spring stop.

[Rivers3Plinker]

I wonder if this could just as easily be accomplished by providing the free space for the hammer to travel independent of hammer spring contact but not preloading the hammer spring? Their are several guns like this that do not burp air behind the shot. I think many FX guns are like this. Just a free floating hammer without the complications of pre-compressing the spring and the extra shock of the spring stop.

I believe Bob mentioned this much earlier in this thread comparing the advantages and effects of the SSG to a shorter, stiffer spring. While similar in some respects, the valve kicking the hammer weight back to the spring still results in some "yo yo" effect as even the stiffer, shorter spring will compress easily at first and send the weight back to the valve wasting some air.

[PakProtector]

Anyone know the thread size of the spring guide on a Marauder (specifically .177 if it matters)?

You can also bore the end cap and thread it 9/16-20...this has the potential to allow a 3" spring because there is a fair bit of wasted space lengthwise in the OE( at least in the Gen1 variant ). Going to do this one today, as soon as I can re-borrow that tap that is... The spring stop will of course get threaded the same, and since I am turning this bit out of brass it will pose me no issues.
cheers,
Douglas

[FuzzyGrub]

Gen II will need a stock modification for the stop to clear. 

[Sfttailrdr46]

Just reread this thread this morning and all I can say is thank you Bob R for choosing to live in the middle of no where. Without the cold Canadian winter you would not have the time to come up with all of your incredible ideas. Usually the math is several steps above my knowledge base but tour mechanical designs are just awesome. Keep on giving me headaches I love it.

[rsterne]

I pulled the SSG out of the Hatsan this morning, and tried changing the springs for the only stiffer choice I had, using two 1.75" long x 0.051" wire springs.... The rifle could not be cocked as the springs went coil bound.... At the moment I'm out of ideas....

Bob

[benzy2]

Anyone know the thread size of the spring guide on a Marauder (specifically .177 if it matters)?

You can also bore the end cap and thread it 9/16-20...this has the potential to allow a 3" spring because there is a fair bit of wasted space lengthwise in the OE( at least in the Gen1 variant ). Going to do this one today, as soon as I can re-borrow that tap that is... The spring stop will of course get threaded the same, and since I am turning this bit out of brass it will pose me no issues.
cheers,
Douglas

Douglas,

If you are still in AA I'm only over in Jackson.  I'd love to see how yours ends up.  I'd like to make a custom back cap but not sure my lack of skills and cheap mini lathe are up to the task.  If you end up with any extras through revisions give me a shout.