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

[Tack Driver 10]

This topic hasn't been active for over a year.
Time to shake things up with the Ghost Gun SSG.
Like a ghost gun it's fabricated almost entirely from plastic.
The sprung weight reduction is scary.
It's ultra light but you don't need a pilots license to take it for a spin...LOL
Made 2 versions, take a peek (pun intended).

[mwgm2020]

Stupid question:  Where or how did you get those parts? 

Also: Ultralites (Part 103) don't need a pilot's license. 

[SILENT SQUIRREL]

Stupid question:  Where or how did you get those parts? 

Also: Ultralites (Part 103) don't need a pilot's license.

Oh no!
Another rabbit hole

Sorry
I couldn't resist

But I too am curious about the parts source and bill of materials.

Edward

[Tack Driver 10]

Stupid question:  Where or how did you get those parts? 

Also: Ultralites (Part 103) don't need a pilot's license. 

I made the parts except the springs and the 2 brass jam nuts are from ACE.
The tan material is peek plastic rod (Ebay) machined on my lathe.

[rsterne]

I wonder how long the plastic parts will put up with the sudden stop of an SSG?.... Mind you, a lot less mass to stop.... Let us know if you ever have a failure, please....

Bob

[Tack Driver 10]

I wonder how long the plastic parts will put up with the sudden stop of an SSG?.... Mind you, a lot less mass to stop.... Let us know if you ever have a failure, please....

Bob

I was a little hesitant to drill out the rod but want to try worst case scenario.
The long SSG rod is made from glass filled peek, GF30.
It's stronger than unfilled peek.
I'll let you know if there's any problem.

Ran a brass SSG vs a peek SSG in my 2617 unregulated PCP.
With 2400 psi the brass SSG made 772 FPS/13.7 FPE, the peek SSG made 820 FPS/15.44 FPE.
Same spring, spacer, .040" gap, 10.34g FX pellets etc.
The brass SSG would make 820 FPS with about .050" of preload.

Put an 1800 psi reg on my 20 cal rat rod gun.
Next will run the brass vs peek SSG.

https://www.gatewaytoairguns.org/GTA/index.php?topic=206234.msg156419768#msg156419768

[Motorhead]

I wonder how long the plastic parts will put up with the sudden stop of an SSG?.... Mind you, a lot less mass to stop.... Let us know if you ever have a failure, please....

Bob

I was a little hesitant to drill out the rod but want to try worst case scenario.
The long SSG rod is made from glass filled peek, GF30.
It's stronger than unfilled peek.
I'll let you know if there's any problem.

Ran a brass SSG vs a peek SSG in my 2617 unregulated PCP.
With 2400 psi the brass SSG made 772 FPS/13.7 FPE, the peek SSG made 820 FPS/15.44 FPE.
Same spring, spacer, .040" gap, 10.34g FX pellets etc.
The brass SSG would make 820 FPS with about .050" of preload.

Put an 1800 psi reg on my 20 cal rat rod gun.
Next will run the brass vs peek SSG.

https://www.gatewaytoairguns.org/GTA/index.php?topic=206234.msg156419768#msg156419768

 Less mass is able to accelerate faster there for yielding a slightly quicker strike on poppet.
Being the mass of the SSG is fixed to the rear cap, its mass/weight is only relative upon release from being cocked and contributes nothing to the hammers mass / weight opening the valve.

[rsterne]

Ron, from those numbers, I would assume then that 820 fps is the plateau velocity at 2400 psi with those pellets.... At 0.040" gap, the plastic SSG allows the hammer to accelerate enough to be ON the plateau, with the brass, is does not.... The potential velocity is the same, the plastic SSG just needs less spring power to get there, which makes perfect sense as less energy is wasted on accelerating the mass of the SSG.... Well done!!!!

Bob

[Back_Roads]

 They sure look pretty, I assumed less mass to accelerate being the gain.

[Tack Driver 10]

The Ghost Gun SSG sprung weight is 1/8 that of the brass SSG.
A reasonable racing analogy might help put things in perspective.

Two cars lined up on the race track, engines roaring, crowd cheering, the championship is on the line.
Car #1 is a 4000 lb yank tank with a 500 HP engine.
Car #2 is a  500 lb  mini rail, same engine etc.

Who would you bet on to win a 1/4 mile drag race?
 

[bnowlin]

May not keep the 500 on the track I would think.  I'm just guessing.
Bob

[Tack Driver 10]

Back to the Future:
27 Dec 2024
Ran the gun regulated at 1300 psi, .040" gap

Brass SSG  13.74g 784 FPS/18.75 FPE
GG SSG      13.74g 804 FPS/19.72 FPE

Brass SSG  15.89g 736 FPS/19.11 FPE
GG SSG      15.89g 762 FPS/20.48 FPE

The GG SSG had a massive amount of hammer bounce.
Obviously overpowering the the valve at this level.

----------------------------------------------------------------

29 Dec 2024
Pumped the 20 cal Rat Rod PCP to 2500 psi last night.
Ran it over the chrony this morning, regulated at 1800 psi. .040" gap.

Brass SSG  13.74g 765 FPS/17.85 FPE
GG SSG      13.74g 880 FPS/23.62 FPE (+115 FPS, +5.77 FPE) 81.3 dB

Brass SSG  15.89g 703 FPS/17.43 FPE
GG SSG      15.89g 826 FPS/24.07 FPE (+123 FPS, +6.64 FPE)

GG SSG      11.42g 930 FPS/21.93 FPE (H&N FTT)


The GG SSG had some hammer bounce so needs tuning.
Clearly the GG SSG outperforms the standard metal SSG.

[rsterne]

Perhaps the GG SSG does not have enough mass to stop the hammer on the rebound from the valve stem?.... The solution may be to use more preload on the spring....

Or, something in between in mass.... Methinks my next SSG will be aluminum.... 

"another fine mess you've gotten us into".... *hands you the shovel to deepen the rabbit hole even more*....

Bob

[Tack Driver 10]

Perhaps the GG SSG does not have enough mass to stop the hammer on the rebound from the valve stem?.... The solution may be to use more preload on the spring....

Or, something in between in mass.... Methinks my next SSG will be aluminum.... 

"another fine mess you've gotten us into".... *hands you the shovel to deepen the rabbit hole even more*....

Bob

Right, the hammer bounce is caused by a weak spring with excessive hammer travel.
HT is .625 plus FF of .040, this coupled with the 2300 spring (.028") is just asking for hammer bounce.
It works good with the standard SSG but add in the extra power of the GG and hammer bounce rears its ugly head.

I think the solution is to first decrease hammer travel to around .500" and maybe a stronger spring.
Might just need shorter hammer travel.
Would be interesting to see how short hammer travel can go.

Looking forward to your new journey down the rabbit hole....LOL

[rsterne]

Remember, you are not getting "more power" from the GG SSG, you are just getting what you could achieve with a brass one with more spring.... The maximum power is a function of driving the valve to be open when the pellet exits the muzzle, for the porting and air pressure you have.... That is what the "plateau" is....

No question, though, the plastic moving parts, having less mass, allows more of the spring power to get to the hammer, as it is a larger percentage of the total mass.... You are wasting less spring power, which allows a lighter spring, or less spring (hammer) travel.... However, if the mass of the moving parts of the SSG are too low, when the hammer is thrown back by the closing of the valve, it will have more tendency to recompress the spring.... You need a certain amount of force/momentum in the SSG to slow the hammer to the point where it doesn't have enough energy to reopen the valve.... If you don't have enough mass, you should be able to replace that with spring preload.... That's my opinion, anyways, for what it's worth....

It might be interesting to lighten the hammer.... That should keep the lift you are getting with the heavier hammer, but decrease the dwell.... If you can get just below the plateau velocity (by the typical 3-5%), you will then have the valve closing when the pellet is 1/3-1/2 way to the muzzle.... This saves air, of course, without losing a lot of power.... and the lock time would be amazing.... The lighter hammer will have less momentum on rebound, so would have less tendency to recompress the GG SSG, and reduce or eliminate bounce....

Bob

[Motorhead]

Yes a lighter hammer, them more hammer spring can yield the same output and generally doing so with even greater efficiency / lower noise & No bounce 

[Hack21]

I recently built my first SSG.  It isn't without it's faults (Ron coined the spring as a "potbelly spring" when in it's SSG-extended and partially buckled state).  It is working great though despite being progressively/inadequately guided. 

My goal was to have a very low dynamic weight and a very long soft spring with lots of preload.  The spring is 0.300" OD / 0.031" music wire / 8 coils per inch and is cut with a free length of 4.45" (this yields a spring rate of only 1.93lb/in).  It has 3.57lbf of preload and is 4.94lbf at the fully cocked position.  The bronze bushing that is driven by the spring is 5.6grams.  I've realized that half of the springs mass is also dynamic (1.5grams in this case).  My hammer is 40.6grams. 

I agree on the merits of a low dynamic SSG mass that have been stated - less hammer spring energy required allowing for a softer spring.  The softer spring allows for less force to cock the airgun.

I agree that more preload should be required to avoid hammer bounce. 

The unmentioned benefit that I desired is that the shot cycle should be calmer with less dynamic mass and spring energy unleashed before the hammer even reaches the poppet.  This can only improve harmonics and be helpful for accuracy.  Also, with a simple trigger mechanism, less spring force improves the trigger weight and this also aids in accuracy. 

Well done Ron, I am excited to see more results. 

[rsterne]

IIRC, you consider only 1/3rd of the springs mass in the moving/acellerating weight.... I can't remember my source for that.... 

Bob

[JPSAXNC]

I wonder if the spring will still vibrate the same on a plastic SSG?

[Tack Driver 10]

Thanks for the input guys.
Your experience and wisdom is greatly appreciated.

The stock 13xx hammer is 38 grams.
Max power is ~890 FPS/24 FPE.
Target is 850 FPS/22 FPE with a lighter hammer.