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

[oldpro]

 Has anyone ever reached 2.0FPE/ci

[rsterne]

Yep, it's been done, but rarely.... Usually only in low powered PCPs, and easiest to achieve if you use tiny sips of high pressure.... When a PCP is set up that way, you would think it is fully shrouded, but it doesn't need one.... Guns like a 12 FPE FT rifle in .177, or a 10M match rifle sometimes hit that level of efficiency.... 

Bob

[oldpro]

So a .25 cal 40fpe gun would be really rare. I'm so so close Bob and I think I have the final piece of the puzzle. Tomorrow I'll send you a string.

[rsterne]

That doesn't surprise me.... I think I was close during some of the SSG installations I have done, but when I cranked the velocity back up to the final tune I wanted I didn't quite make it.... but with a 50% improvement over previous I didn't really care.... It won't be long before we start seeing 1.5 FPE/CI as the new standard instead of 1.0-1.2.... so it just makes sense that instead of thinking 1.5-1.7 as being outstanding, we won't get excited until we push close to or exceed 2.0 FPE/CI....

Bob

[lloyd-ss]

I added more photos to Post # 456 about Harry's Excalibre....

Bob

Bob or Harry, Does the Excalibur have a handle on the hammer assembly, and a separate bolt handle, also?
Thanks,
Lloyd

[Gippeto]

Google image search turned up a few pics of the other side....this was a nice one. 



Al

[rsterne]

I'm guessing the crescent shaped slot in the rear top of the hammer "cage" drags a bolt back with it to work the magazine and load the chamber....

Bob

[SpiralGroove]

Hey Guys,
Irregardless of its efficiency, that's one beautiful gun!!! 

[OZ Harry]

I'm guessing the crescent shaped slot in the rear top of the hammer "cage" drags a bolt back with it to work the magazine and load the chamber....

Bob

Bob is spot on. Why am I not surprised?
The loading shaft has a latch which fits that other slot.  When it is pulled back out through the magazine there is also a little spring loaded finger/lever operated to pivot and index the magazine. Then the forward cocking stroke allows for the next pellet to be loaded. In all the tens of thousands of shots mine has never malfunctioned.  The new Polymag shorts also function perfectly.

SG, that stock on my Excalibre page 23 is grade 3 Turkish walnut. They did come with grade 4 too!

I want to publicly thank Bob for his time and effort in presenting those pics and in succinctly summarizing my explanations so accurately.
Thank you Bob.
Regards to all, Harry.
 

[PakProtector]

I got a string measured, 10 shots long, 82 fpe average, and used 300 psi, or 1100 ci of air. SSG gap of .050-.060", velocity centered on 965 fps and 40 gr cast boolits from a 225107 mold. That is ~.75fpe/ci with a 23" barrel. I was hoping for better... I lost my notebook I kept track of this one with, so I can't provide data for a proper conversion. I remember its string being longer, but also using more air( larger delta-P) with the standard spring installed.
cheers,
Douglas

Was having some issue with such a poor result, and ran a few more strings. Took an average of air consumption, and got a result 50% higher...not so bad anymore. Threw out highest and lowest...LOL

[Rocker1]

OZ Harry I laughed when I seen Wollongong, thought you were joking  but wife is from NZ and said she has been there.  David

[Froggy.]

Bob, thanks for sharing this mod! It totally transformed my crosman 1377 pcp. I'm using a very soft valve spring... Only 200gram...and hammer bounce was a real issue.
With the SSG it's all but nullified.
Efficiency went from 0.8 to 1.57 fpe/ci.
Shot string from 1600 psi to 1340psi.
10.34 jsb's. Un regulated... Just a quick shot string with the transfer port fully open.. 4mm...barrel length 16inch.
882 884 888 880 893 883 880 879 880 881 884 882 889 893 895 894 905 901 892 890 903 893 899 893 894 897 890 891 891 880 883 884 875 873 875 869.
Should get 50+shots from 1800 psi with more preload and reduced tp.

[rsterne]

I pulled apart my 2560 today and swapped it over to the new style one with the internal stop.... Here are the old and new parts....



I am now using a 10-32 machine screw with a piece of 7/32" OD tubing slid onto it for the guide.... Then you slide on the spring and an aluminum collar that hits the end of the gap adjusting bolt when cocking the gun and compresses the spring.... The stop nut is turned from a piece of 5/16" rod, drilled and tapped 10-32 and tightened against the end of the brass tube.... I start out a bit longer than I need and keep shortening the tube until I can get the gun shooting on the plateau with no gap.... Once I get the right length, I install the stop nut with a drop of blue Loctite, tightened against the end of the tube.... The stop nut has a slot in the end for this purpose.... The gap adjusting nut is drilled just over 5/16" because the stop nut has to slide through it.... The end cap is tapped 7/16"-20NF for the adjusting bolt, and then counterbored just over 7/16" to miss the cocking collar.... At the bottom of the photo is the original SSG I made.... You can see how much shorter the new guide is.... Below is the new SSG assembly, ready for installation....



When the gun is uncocked, the stop nut is recessed about 1/2" inside the gap adjusting bolt, so you can't see it.... Compare this with the one above, where the stop nut and bumper O-ring (no longer required) are outside the gap adjusting bolt.... Below is what the gun now looks like when cocked....



This installation is much cleaner, and there is no way you can pinch your fingers like could happen with the old one.... However, you still have a cocking indicator because the stop nut (the part with the slot) is visible when cocked.... With no gap I had about 985 fps, which I could adjust down to whatever I wanted.... At 1-1/2 turns out the velocity was just over 900 fps and the gun was very quiet.... I ended up about 1 turn out, with a average velocity of 960 fps, the same as I had before.... I might have lost a couple of shots compared to the first SSG, but I have still gained about 40% more shots per fill than without the SSG.... and I no longer have to worry about pinching my fingers and I can wrap my thumb over the wrist of the stock again because is it so much more compact.... The efficiency is around 1.40 FPE/CI....

Bob

[Ribbonstone]

Can see where a longer spring/longer stroke is going to be needed.  Just going to need a longer stroke/longer spring/ stronger spring.

Just using the standard stroke with a 2260/2240 type end cap isn’t going to get any real power unless the spring is super-stiff. If I want more power am going to have to make a longer rear end cap, deeper recessed, in order to fit a longer (likely stronger as well) spring in order to increase the stroke.

SSG has potential, although the early results using 2260 length springs/stroke are a little mixed.  Have actually gone DOWN in efficiency from the previous tests, but picked up energy per shot.  Over all, the efficiency and shot count has increased.
 
Tested with a pair of 2260 conversions.  A .177 version (left) and a .22 version (right). Only 72-73cc's of air, so the shot counts won't be massive:

 

Simplest SSG version:




Long bolt, end cap with a hole, shorter/stiffer spring, o-ring, lock nut, and a 2nd lock nut (in this case a kind of wingnut).

Assembled it looks like this:





THINK the idea is to keep the spring tension off the valve stem, so that any opening of the valve is just by the inertial of the striker.  So as you adjust the lock nuts IN, the spring gets shorter, and there is less and less tension on the striker as it contacts the valve stem.  Think of it as a “sling shot” striker.




So to adjust it for these tests:

1.   Adjusted the lock nuts out.
2.   Pulled trigger.
3.   Whacked the end of the adjuster with a stick.
4.   If the valve opened even a little bit, adjusted the lock nuts "IN” until the valve didn’t open at all.

So this set it to about .052” of striker stroke. More than that, and the valve would (weakly) open when the adjuster was struck.

AM POSITIVE there is more to be gained by adjusting them in small increments.


But as a gross head-to-head test:

Shots with the lock nuts totally out of play (adjusted way-way back):

.177/2260:

 9.3gr. WC  / 25 shots inside of 4% (from 725-696fps) / 10.4 foot pounds / efficiently of 1.15 FPE/cuin

.22/2260

15.9gr. JSB / 24 shots inside of 4% / 14.2 foot pounds / efficiency of 1.38 FPE/cuin


Everything the same as above, just the SSG adjusted. With the adjuster set as described above:

.177/ 2260

9.3gr. WC / 42 shots inside of 4% / 657 – 631fps / 8.6 foot pounds / efficiency of 1.4 FPE/cuin

.22/2260

15.9gr. JSB  / 30 shots inside 4%/ 672-645fps / 15.3 foot pounds /efficiency of 1.58 FPE/cuin

 MIXED REVIEW:

BOTH of them dropped their sweet spot from 2100psi to 1800psi.  That’s pretty well proof of a lighter striker hit to the valve.


The RANGE of pressure was about the same. Without the SSG adjusted as listed, sweet spot ran about 2000-1000Psi.  With the SSG adjusted, sweet spot ran about 1800 – 800psi.

The .177’s energy went down by about 16% and the efficiency went up by 22%...which seems pretty darned close to even to me.

The .22’s energy went up by about 8% AND the efficiency went up by about 15%, which is definitely a “win”.

EXPECTATIONS:

Now likely there will be an adjustment that would get the .177 back in line. It always seems to be those little 1/8th -  1/4th turn adjustments that do the trick. I’d hope for BOTH and increase in energy and at least the same efficiency, but I’ll have to work at it.

Might be that a standard weight 2260/2240 striker would do better than a lighter weight striker. If I got the idea right, it’s about a striker hitting the valve without ANY spring tension, so a heavier (standard weight) striker might be in order. Both of these have been lightened.

Going back to a full sized transfer port would up the air flow. Might detract from shot count, but would increase the energy per shot…have to balance that.


It certainly looks like there is something to be gained here.  Likely it is a reduction in the hammer bounce issue that’s increasing the efficiency.




It certainly looks like there is something to be gained here.  Likely it is a reduction in the hammer bounce issue that’s increasing the efficiency.

[clgraham82]

I pulled apart my 2560 today and swapped it over to the new style one with the internal stop.... Here are the old and new parts....



Bob

Bob are you still using the 1.75" x 0.040" wire spring for this one?

[rsterne]

That gun has always used a QB spring, in all three versions, original, first SSG, and new SSG....

Bob

[Gippeto]

Had some "personal time" in the garage this morning...






And a bit more time in the garage after supper.

Scrounged up enough parts to assemble an otherwise stock-ish 2240. No chrony numbers tonight, but does flush a 14.3 CPHP in a well seasoned 2x4. First test shot had a bit of the usual BRaappp...turned the adjuster bushing out a half turn and....GONE. Crisp snap to it now like I've NEVER heard from a 2240.

Still need to trim the guide rod to length and add a screw driver slot to it...and make a proper pin spanner to adjust the bushing...already scratched the brass turning the bushing with a screwdriver. 

Curious to see how fast it's actually running...and how many shots per cartridge...tomorrow.

Thanks Bob.





Al

[sawtoothscream]

anyone do this with a marauder .25?   

[oldpro]

anyone do this with a marauder .25?

http://airgunguild.com/index.php/topic,11.0.html

[aceflier]

Hopefully someone gets an instructable video up for those of us with ADD.