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

[shorty]

I thought maybe this may help with some of the SSG designs.

https://www.google.com/search?q=recoil+spring+guides&biw=1454&bih=680&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjA--T5lbHKAhXEOj4KHTGmDjEQsAQIIg#imgrc=_

[rsterne]

I rebuilt the first gun (2260/Disco) I converted to the SSG today, using the last drawing in Post #356 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 much shorter guide, with 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

[Airsnipe]

Since the spring assembly is now traveling with the hammer, there would be no reason the hammer spring assembly could not be built into the hammer assembly with the same kind of results. You could possibly thread the spring guide into the hammer and with a cap head the spring preload could be adjusted from the rear without disassembly.

[Motorhead]

So HOW do you now adjust spring preload ?


It looks like nut on stop rod would be further tightened .... then collar screw would be tightened down equally until gap distance is in place once more.

Is it that simple

[rsterne]

I have tried spring guides that travel with the hammer, they are used in rear-cocking hammers, for example.... There is an example of an SSG like that in Post #356, suggested by I_like_Irons.... It is critical that they be threaded perfectly as they must be 100% concentric with the hammer or they will bind in the rear guide.... Unless required for rear-cocking, I prefer the loose guide, with a shoulder on the front of the guide captured between the end of the spring and the hammer.... I have used that setup a lot.... It adds the weight of the guide to the hammer strike (an easy way to make it heavier to gain dwell), but with no alignment issues.... This version of the SSG has that advantage, plus the spring can be easily removed to change it.... Unfortunately, since the collar hits the rear plug on cocking, you do have to remove the rear plug to change springs, but you don't have to pull the hammer....

Yes, Scott, you adjust the spring preload by how far the stop nut is threaded in towards the front of the guide.... I always have a target in mind, so I just keep threading the guide further and moving the nut down, always tightening it against the shoulder on the guide, until I can hit just over the power I want, and then fine tune with the gpa adjuster (which in this case sets the position of the cocking collar)....

Bob

[musquat]

I can report that the bstaley design does work!  Apparently you have to have at least 20 posts before you can insert pictures, so I will post several short descriptions so that we can get to the photos.  The vehicle for this mod is a .22 Crossman 2400kt with an 18"barrel.  It has a 17 CI tank regulated to 2000psi, with poly TP and standard valve mods.

TBC

[musquat]

My pre-mod string was from 2500psi to 2000psi using 14.3 CPHPs.  Average velocity of 861 giving an efficiency of .76FPE/CI

[musquat]

That first test had an Extreme Spread of 26 fps which if I calculated correctly is 2.9%.  My post mod string also started at 2500 psi and lost a little velocity-down 40fps to 821.  But it more than doubled the efficiency to 1.69 PFE/CI!  Way better than I was hoping for.  The best part was the usable shot count.

TBC

[musquat]

I went from 19 shots to 60 with an ES of 32 fps, which I calculate at 3.8%  How on Earth did I triple the shot count? I think the regulator setting comes into play

[musquat]

The regulator was set just in front of the knee of the velocity ark, so that the velocity just started to fall after the regulator pressure was crossed.  After the mod, When I shot down past the 2000 psi mark, the velocity started to climb, peak and finally really started to drop after 60 shots, which put me at about 1850 psi.  Yeah I know I kinda cheated by using more air, and if I was unregulated I wouldn't have tripled my shots.  But I continued the string until the extreme spread made sense to stop.

[musquat]

On to the build.  With my very limited machining skills, making a hammer was by far the most ambitious thing I have attempted.  I copied the dimensions of the stock hammer, except I didn't cut a waist into it, as I am using a PROD trigger group.

[musquat]

I found a rod that just fit through the spring.  Actually a tension rod from a snare drum-did I mention I repair instruments during the day? 

[musquat]

Sorry to be posting so much... I really want to show the pics :-)  I drilled the hammer to fit the rod, and countersank the head into the front of the hammer.

[musquat]

The spring cavity measures the same depth as the OEM hammer, so I have the same hammer stroke as before.

[musquat]

There was no need to make the guide channel longer because the head of the guide aligns the rod when not cocked. Actually I think it could possibly be drilled deep if you needed to make more room for your stop nuts or wanted to use a longer spring.

[musquat]

I was using a Disco spring, so I had plenty of room. 

[musquat]

I am still using the 2300s RVA, so the back looks very tidy.  I also discovered that the RVA doubles as a degasser since the guide rod runs from it to the valve stem.

[musquat]

Surprisingly enough, after I finished the new hammer, it weighed exactly the same as the old one-58 grams.  With the rod, spring, nuts, and cocking pin added, it totalled 71 grams.

[musquat]

Forgot to mention that the string I shot was with the gap set at 1/2 turn out from touching the valve stem, and the spring just shy of coil bind.

[musquat]

My next experiment will be to lighten the guide rod by using a much smaller diameter rod with a plastic or delrin sleeve.