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

[Blue]

thelast88, +1 thanks for the pics.  And super duper thanks for the tip on drilling the cap from the back to keep it centered!

Blue

[Ribbonstone]

Working on the lower power end, but it's been educational.

Test rifles: (.177 left / .22 right):



Simple SSG:





Looking for the most shots for the least air use, pretty much ignoring energy.

Tried for a more exact efficiency calculation, taking my time to get accurate readings of the fill pressures and limiting the  test to the sweetest of the sweet spot (trying to only test in the top of the curve, avoiding the up and down slope of the graphs).

Been adjusting in small steps, just getting velocity readings, looking for the best air use and ignoring power (for the time being).  No doubt about it, lower power is more efficient with these two.

Ended up that really low power would need some more mods (smaller transfer ports would be my guess).  Past a certain level, the velocity became more erratic with occasional wildly slow or wildly fast shots cropping up. That “certain level” seemed to be about 7 foot pounds for the .177 and about 10 foot pounds for the .22.

Didn’t notice the erratic velocity swings at higher energy levels, but efficiency quickly decreased.


So for the efficiency test, stayed in the low energy area and just tuned for the best shot count/energy ratio I could find.

The “CHEAT” for high efficacy numbers is to stay in the best-of-the-best pressure range (the sweetest of the sweet spot).  The low speed shots at the up slope and down slope of a graph tend to pull the average velocity down.

So I stuck to the 30 shots either gun can give in the best middle range.

Filled each to 1900psi.

Shot 30 shots on target getting velocity readings.

Checked remaining pressure after the 30 shots.

.177 test:


.177/2260 ended up at 1400psi (so 1900psi to 1400psi of air used from a 72cc volume). The 8.4gr JSB’s in the .177 had a high of 687fps and a low of 670 fps in those 30 shots (spread of 18fps over 30 shots...about 2 1/2%). That’s only 8.6 foot pounds, but a good string of 30 shots for a non-regulated little rifle.

 .22 test:


.22/2260 ended up at 1300psi (so 1900psi to 1300psi of air from a 76cc volume.  This was a prototype HiPac unit that was a little bit longer than what became standard).  The 15.9gr. had a high of 578 and a low of 563 in those 30 shots (a spread of 15fps over 30 shots...about 2 1/2%).

Works out to about 1.7 FPE/cuin for the .177 and 1.8 FPE/cuin for the .22.

(BTW: Rather than look at the accuracy as a .177 vs .22 thing, look at it as an LW barrel (the .177) vs a Crosman  barrel (.22) thing.)

[Gippeto]

Going to pull mine out of the 2240 sometime this weekend and pop it into a .177 cal 22xx ish pcp (custom tube and internals). Current tune is 22 shots from (fps) 700 to 725 and back to 700  w/10.3gr JSB on a 2000psi fill.

Already pretty quiet and no perceptible bounce...curious to see what happens.



Al

[Ribbonstone]

Work in progress.

Remind me of 2 things:

1.   I really need to pressure wash the patio.
2.   This old .177/2240 HiPac conversion needs a little up-keep/refinish.



Just started work with the SSG, but it’s showing promise.

[Motorhead]

I am already seeing the set up gap decreasing some as the buffer o-ring gets crushed from the static pressure against it while action is not cocked ... So may i suggest this 

THIS IS NOT picking on any ones application ... but one to flag you guys on something personally felt needing addressed 

Those doing the conventional stop rod out the back ... BUFFER O-ring/s should really be captive to some degree on there O.D.
As an o-ring gets crushed between flat surfaces it GROWS IN DIAMETER as it becomes thinner from the crush.
By containing o-rings O.D. in a cup, thimble or counter bore you stop its outward expansion and keep the height more stabilized.  Crush can still happen, it just does so inward and rings profile changes to a semi square rather than a pancake

Talking this ...

In the case of a double stack o-ring they will climb over one another and WILL NOT maintain there height so critical to maintain the gap needed.  Suggested cup/thimble only needs to be @ 2/3 rds o-ring cross section to support it.

* This outside diameter can also be a simple counter bore in the end cap where o-ring comes to rest.
Something like this ...


Anywho ... just suggestion on some finer tuning the parts of the system to get better long term consistency from your SSG set up 

Scott

[oldpro]

 WOW guys lots of fine pics to see this morning! Outstanding work BRAVO!!

[zaphod621]

Those doing the conventional stop rod out the back ... BUFFER O-ring/s should really be captive to some degree on there O.D.
As an o-ring gets crushed between flat surfaces it GROWS IN DIAMETER as it becomes thinner from the crush.
By containing o-rings O.D. in a cup, thimble or counter bore you stop its outward expansion and keep the height more stabilized.  Crush can still happen, it just does so inward and rings profile changes to a semi square rather than a pancake

Scott

An easy way to make the cup for the o-ring is to use a nylock nut and grind the nylock end flat and thinner then remove the nylon insert and place the o-ring in the cup remaining. Of course you loose the locking feature of the nut but using a jam nut solves that.
I am liking this simple SSG on my 2300kt. I am only using it as a hdd and it works well on the pistol.
Brian in AZ.

[oldpro]

 Im not seeing many chronograph readings posted come on people lets see some before and afters. Thats where the light will shine.

[shorty]

Completely agree. I would really like to see those numbers with pressure usage.

I would really like to see Scott run a 1.8 (or greater) efficiency with a regulated .22 cal tuned around 20fpe. With a 3000  psi charge and 1000 psi reg setting.He should see nearly 150 shots on 1 fill under 2% ES.

Now that would make me buy a regulator.

[Motorhead]

Completely agree. I would really like to see those numbers with pressure usage.

I would really like to see Scott run a 1.8 (or greater) efficiency with a regulated .22 cal tuned around 20fpe. With a 3000  psi charge and 1000 psi reg setting.He should see nearly 150 shots on 1 fill under 2% ES.

Now that would make me buy a regulator.

 

Sadly a .22 at 20 ft lbs is going to be not much different than a .177 at the same power.
Granted the larger bore "should be" more efficient, don't see it making that much different when we're already sipping such small amounts of air.

Taking Reg set point down to 1000# uses more air per shot and likely would require valve to be larger yet in port sizes to utilize this lower pressure.  While you gain @ 600# more air to use, your using more per shot and not sure results would be any better ... and doubt they would be.

[shorty]

Scott don't sell it too short yet. You would be the king of kings with that shot count.

I can already do 70 shots at at an average 22 fpe from 2200 psi to 1200 psi with my dual wire spring at 1.8 efficiency. I ran the numbers on Lloyds calculator and at 180cc (marauder with regulator) you should hit 150 shots from 3000 psi to 1000 psi using a regulator set at 1200 psi with a plenum of 1/2 fpe per fpe along with a transfer port sized correctly and valve spring on the heavy side.

[Motorhead]

Scott don't sell it too short yet. You would be the king of kings with that shot count.

I can already do 70 shots at at an average 22 fpe from 2200 psi to 1200 psi with my dual wire spring at 1.8 efficiency. I ran the numbers on Lloyds calculator and at 180cc (marauder with regulator) you should hit 150 shots from 3000 psi to 1000 psi using a regulator set at 1200 psi with a plenum of 1/2 fpe per fpe along with a transfer port sized correctly and valve spring on the heavy side.

Not to clutter this thread .... Don't have an M-rod to try this on ... Both my .177 & .22 are already highly tuned and NOT getting fiddled with further.

[shorty]

That's too bad Scott. There's nothing like having the best of the best.

Most people before Bob shared the SSG was happy with a .9 or 1.1 efficiency. Heck, I tried the short stiff spring last year with efficiency over 1.5 with proven results.

Your the go to guy with the reg set ups and resources for regulators.

[quickster47]

Scott thanks much for the tuning advise/heads up on making the best use of the O-rings.  When I am making my endcap pieces for my simple SSGs I will take that into consideration.

Carl

[thelast88]

Those doing the conventional stop rod out the back ... BUFFER O-ring/s should really be captive to some degree on there O.D.
As an o-ring gets crushed between flat surfaces it GROWS IN DIAMETER as it becomes thinner from the crush.
By containing o-rings O.D. in a cup, thimble or counter bore you stop its outward expansion and keep the height more stabilized.  Crush can still happen, it just does so inward and rings profile changes to a semi square rather than a pancake

In the case of a double stack o-ring they will climb over one another and WILL NOT maintain there height so critical to maintain the gap needed.  Suggested cup/thimble only needs to be @ 2/3 rds o-ring cross section to support it.

Anywho ... just suggestion on some finer tuning the parts of the system to get better long term consistency from your SSG set up 

Scott

Pictures and some of the text removed to reduce the size of the post.

Scott, I know what are you talking, but it's just me experimenting, and, I really don't have any problem with two o rings stacked.
The spring are relatively low power and the o rings are tight on the rod, it didn't climb one over another in 100+ shots.
I will probably remove one of them a leave one alone, then shorten the rod for the width of that o ring and that's it.

Anyway, thanks for suggestion.

[Motorhead]

Well did another SSG devise today on the TM-1000 FT gun.  This one done having end of stop rod travel down into hammer body when cocked ( removing the kinetic striker & spring using its bore ), floating washer to be the stop shelf, spring support while other end of rod into a fixed base at tension adjuster cap.
NOTHING comes out the rear upon cocking with gun looking and acting 100% stock.   And yes, it works 

That makes all the personal PCP rifles able to be SSG converted done.  Dang what a great devise !!

[Sfttailrdr46]

  Ok so now somebody needs to start making some of the better designs to sell to those of us with no machine shop access and I would love to get one of the invisible designs for my .25 Marauder that is beginning to be a project rifle.

[aPpYe]

Taking Reg set point down to 1000# uses more air per shot and likely would require valve to be larger yet in port sizes to utilize this lower pressure.  While you gain @ 600# more air to use, your using more per shot and not sure results would be any better ... and doubt they would be.

Hi Scott, I will admit that I have never actually counted shot strings, but I am curious, is there a rule of thumb to go by when it comes to pressure vs efficiency and shot count?  I am running a regulated .177 2400kt with a 24" barrel.  The goal was to be able to push 10.34gr JSB heavies at 900fps, while on the knee of the curve.  Originally, I was running at 1400psi, as suggested by rsterne, but then I lowered it to 1200psi and was excited that I was still able to get 900fps.  Then I lowered it again to 1050psi (1100 with the bottle filled, and 1050 when just above set point), and am just barely able to achieve 900fps with these pellets.  Granted, I am using more spring preload to achieve these results, but my thought was that since the air is at a lower pressure, it would be escaping at a lower rate, cancelling out the longer/wider dwell.  Again, I have never actually counted shot strings.  I thought this automatically equaled higher shot count, but your post contradicts this.  When I shoot at 885fps, I am somewhere on the knee of the curve with 1000psi...

[rsterne]

Efficiency per shot on PCPs tends to go up with pressure, for a given FPE.... In a regulated PCP, however, the "headroom", or the difference between your fill pressure and setpoint pressure goes down, reducing the overall amount of air you have available.... Finding the best balance between the two will give you the most shots at a given FPE.... As you reduce the pressure (like aPpYe is doing), you will eventually get to the point that you cannot get the FPE you want, or you will be operating up on the plateau of the curve where the efficiency is terrible.... and even though you have more headroom (air) available, your shot count will drop.... This has nothing to do with SSGs, of course....

Bob

[aPpYe]

Whoops!   I apologize for that!   Somehow I got the idea I was quoting from my 2400kt thread.  In no way do I want to hijack this thread!   Again, sorry about that Bob.   I will continue discussion in my own thread.