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

[triggertreat]

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.

4.5% below max should turn out to be a great tune.  Nice and quiet and efficient.

[rsterne]

I have ordered some 3, 4 and 5mm 6061 aluminum rod and aluminum nyloc nuts to fit from Amazon.ca.... I will make the forward pusher/guide from Delrin (currently aluminum), and try the SSG on my .25 cal. regulated Carbine with the same spring initially.... It is tuned at 919 fps on a 935 fps plateau with a 105 g. steel hammer and 3/16" steel SSG, at 2.1 turns of gap (0.105") and about 0.4" preload.... The lighter SSG should put me on the plateau immediately.... I have a lighter hammer and 2 lighter springs available to try....



I will weigh the existing parts (including 1/3 of the spring), and the new parts when I make them, and we'll see what happens....

Bob

[Hack21]

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

Bob

You are correct Bob.  This was not intuitive to me, but you schooled an engineer on this one.  Well done! 

I am glad to see you are getting in on the lightweight SSG action.  I am excited to see your results as well.  It should pair well with the longest and weakest spring possible. 

[rsterne]

I made the same mistake (using half the mass) until I read that.... Google AI confirms it is 1/3, BTW.... I wonder if the same thing applies to the moving column of air behind a projectile in a barrel.... and if the conditions are the same for valve open (air mass being added) and valve closed (the air spring is expanding).... I'm guessing not.... Methinks I'll pass that on to Lloyd to ponder....

Bob

[Tack Driver 10]

Have this 14 gram hammer from a previous experiment.
Reworked the core and put it in the gun.

14 gram hammer
13.74 725 FPS, 16.03 FPE .040" gap
13.74 760 FPS, 17.62 FPE .000" gap

Made a new 20 gram hammer from peek (what else).
13.74 806 FPS, 19.82 FPE .040" gap
13.74 827 FPS, 20.86 FPE .000" gap
15.89 745 FPS, 19.58 FPE .040" gap

Might trim the nose of the hammer to get another .100" hammer travel, currently .550".
That should increase the power some.
Didn't detect any hammer bounce so I think that problem is solved.
Thanks to all for the light weight hammer suggestion.
GG SSG uses a disco spring. (disco is not dead....LOL)

That's all for today folks.
Now I'm going to party like it's 1999....LOL
Happy New Year!

[Tack Driver 10]

Decided to trim both hammers .090" making them flush with the face.
Will the decreased weight offset the gain of the increased hammer travel?

The 14 gram hammer now weighs 12.4 grams with .640" HT (vs .550").
The 20 gram hammer now weighs 18.8 grams with .640" HT (vs .550").

Ran them both over the chrony with 13.74g FX pellets, same disco spring.

14.0g hammer, .550 HT, .040" gap, 725 FPS, 16.03 FPE
12.4g hammer, .640 HT, .040" gap, 775 FPS, 18.32 FPE (+50 FPS, 2.29 FPE)

20.0g hammer, .550 HT, .040" gap, 806 FPS, 19.82 FPE
18.8g hammer, .640 HT, .040" gap, 840 FPS, 21.52 FPE (+34 FPS, 1.7 FPE)

Total sprung weight:
Original hammer/ brass SSG
41.0g+22g=63g

Light weight hammers/GG SSG
12.4g+2.7g=15.1g
18.8g+2.7g=21.5g

[Tack Driver 10]

This is a little off topic but relates to the mass/sprung weight issue.
How about reducing the sprung weight of the valve stem components.

A ghost gun stem made entirely from peek with a pen spring to hold it closed.
Seems less hammer strike would be needed to fire the valve.

A 5/8" hammer made entirely from peek would weigh about 6 grams.....hmm
Stem measurements are in grains, 15.43 grains=1 gram.

Thoughts?

[JPSAXNC]

Going to light on the valve return spring might increase the peak of the bell curve.

[Tack Driver 10]

Sadly this dog won't hunt....LOL

Although peek seems very hard it's soft compared to steel.
Tested the peek stem at 2000 psi and it absorbed energy and was much more difficult to fire.
Drill blanks with a peek/pei seal seem to rule the roost for valve stem material.

[JPSAXNC]

I made a light weight SSG by using a piece of thin walled SS. tubing instead of a solid rod, buy brazing a small threaded end cap into one end and a piece of threaded rod into the other end.

[Motorhead]

Yes yes yes ... Lighter than OEM weight hammer, sometimes altered stroke, a somewhat heavier spring within the SSG devise is the ideal configuration !!
It does take some fiddling to find the XYZ of the parts that balance it all ? .... those who are fiddlers it is well worth the effort 

[Rocker1]

  Here we go  again lol!!     There for awhile we had a lot of configuration's going on with hammers and ssgs.  David

[Tack Driver 10]

Going to try to make this my last post on the GG SSG.
Don't want to clog this thread (too much) with gun specific results.

The valve that was in the gun had a .220" throat and .275" diameter Mrod stem.
Replaced the valve with a peek stem version, .230" diameter, pen spring.
Concave 150 degree seat with a .200" throat, same .170" port.
The peek stem fires much easier than the Mrod stem.

Regulated at 1800 psi, .560 HT, 13.74 FX pellets
12.4g hammer increased +60 FPS, 2.78 FPE, 725->785 FPS
18.8g hammer increased +76 FPS, 3.93 FPE, 806->882 FPS

Made a new 10.4g peek hammer

Regulated at 1300 psi, .560 HT, 13.74 FX pellets
10.4g hammer 706 FPS, 15.20 FPE
12.4g hammer 795 FPS, 19.20 FPE (slightly more than @1800 psi)
18.8g hammer  815 FPS, 20.26 FPE (max pwr at 1300 psi)

Would like to regulate this down to standard PB 850 psi.
Might be interesting to see how light the hammer can be.
A pure solid peek hammer would weigh about 6 grams.
Might have to make a hammer from Styrofoam....LOL
How low can you go?

[Motorhead]

LPHV does not work well for the velocities we typically seek with Air guns.  Been there / Tried that 

[Tack Driver 10]

Removed the brass core from the 18.5g hammer.
Replaced it with a peek core and short 10-32 setscrew striker.
New hammer weighs 6.83g, total sprung weight 10.51g.

With 13.74 FX pellets, .560" HT
1300 psi, .040" gap, 590 FPS, 10.62 FPE
1000 psi, .040" gap, 590 FPS, 10.62 FPE
0850 psi, .040" gap, 595 FPS, 10.80 FPE
0850 psi, .000" gap, 625 FPS, 11.92 FPE
0800 psi, .025" gap, 585 FPS, 10.44 FPE (drop off)

Can be fine tuned by varying hammer weight and HT.
Decent power considering the ultra light hammer.
Makes for a nice 850 psi regulated <12 FPE shooter/pester.
With heavier hammer and increased pressure has made up to 24 FPE.

Very pleased with the test results using this gun and GG SSG.
Thanks again for those that chimed in with great advise.

[rsterne]

My aluminum rod arrived yesterday, so I took out the steel SSG from my .25 cal MRod Carbine, and replaced it with one made from aluminum and plastic....  The original SSG moving parts (3/16" steeel rod, aluminum guide, steel nuts) weighed 20.2 grams, plus 1/3 the weigh of the spring (7.1 / 3) = 2.4 grams, for a total of 22.6 grams.... The new lightweight SSG moving parts (4mm 6061 rod, teflon guide, aluminum nyloc nut) weighs 7.7 grams, plus 1/3 of the spring = 10.1 grams, just 45% of the original.... I adjusted the preload the same, and installed the new SSG and plotted the velocity vs. gap on the same graph as before.... The blue line is the aluminum SSG, the red line is the original steel one....



It is obvious that not only does the lighter SSG produce the same velocity with a greater gap (less spring compression), but actually had a bit higher plateau (maximum velocity) as well.... Certainly more of the spring energy is going into opening the valve, and the lower total mass means the valve will be opening faster at maximum power.... The downside was that the gap for the power required is now larger, over 1/8", which is getting too big for the best hammer consistency.... I had a lighter spring, made from 0.051" wire instead of 0.055", and I replaced the original after checking the preload, which was 3.8 lbs.... I adjusted the lighter spring to the same preload, did some testing, and then increased the preload to 4.5 lbs but still ended up with lighter cocking effort.... This produced the curve in green above.... With zero gap I could still get to the maximum with the heavier spring, but the SSG was now much more sensitive to the gap.... I could get my desired velocity with just under 1.5 turns of gap (about 0.070"), with a virtually flat velocity string from 3000 psi down to 1600 (reg. setpoint is still 2000 psi).... The highest velocity of the 24 shots (3 mags) was 926 fps and the lowest was 917 fps (an ES of just 9 fps, or 1%).... The average velocity was 921 fps (47.5 FPE) and the efficiency ended up at 1.32 FPE/CI, which is great....

I am delighted with the new lightweight SSG, and from now on I will probably make them all this way, with an aluminum stop rod and a teflon spring guide....

Bob

[Tack Driver 10]

Great results Bob.
1.32 FPE/CI is amazing at that power level.

I used an ultralight SSG with a peek valve stem vs Mrod stem.
That allowed a 50% reduction in hammer weight.
Even more at lower power levels.

[rsterne]

Yes, I have been following your tests closely, they were my inspiration for this change.... My hammer is 105 grams, and I thought I had a lighter one, but it was shorter and the hole for the spring (guide) was not deep enough and could not be easily altered.... I got to minimum gap with just changing the SSG and spring, with great shot-to-shot consistency (1% max over 24 shots), and great efficiency, so I'm going to quit while I'm ahead....

The next two guns I build (my Benchrest twin bottle guns) will have SSGs made from aluminum, right from the get-go.... Thanks for prompting the new direction for the SSG....

Bob

[Motorhead]

Bob,
It is good to read that you are realizing the potential of having lower mass within the SSG devise no matter the style applied.
Have personally always tried to go as light / low mass as practical in my now @ 9 years of making these devices in well over 20 different PCP rifles & pistols.

And MUCH credit goes to Bob for the years of inspiration to continue using variants of the concept

Then came the Balanced valve R&D years ... where, the SSG really came into play being vastly superior to a free flight hammer that would double tap or greater the easy opening properties of such valves.

THANK YOU BOB 

[rsterne]

Oh, I realized that lowering the mass of an SSG would increase the percentage of spring energy delivered to the hammer, my comparison of the different types waayyyyy back talked about how each type was different in that regard.... It follows that being able to use a lighter hammer spring in some cases may result.... I was just too lazy to change systems (PCPs) that were already working well for relatively small changes in performance.... My latest gun was a good candidate to experiment with, and the results were worth the effort....

Bob