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Mobley0317 · Member

So Bob I'm in the same boat as Fritz. How much would that contraption cost if you were to sell it as is??? I'm looking at 22xx PCP but I dont think I'm mechanically minded enough to pull it off on my own. Actually I know for a fact that I'm not mechanically minded enough Laughing

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rsterne · Moderator

Fine tuning today.... I set the gun up with the adjuster out 2 turns, pumped it to 3000 psi, and then worked on gradually increasing the port sizes.... I was using JSB Heavy 18.0 gr. pellets, with the following results for 5-shot strings:

Barrel Port 0.166", Transfer Port 0.161", Valve Port 0.161"; 868 fps, SD 3.6
Barrel Port 0.166", Transfer Port 0.166", Valve Port 0.161"; 872 fps, SD 4.0
Barrel Port 0.169", Transfer Port 0.166", Valve Port 0.161"; 874 fps, SD 4.3
Barrel Port 0.169", Transfer Port 0.169", Valve Port 0.161"; 878 fps, SD 3.9
Barrel Port 0.172", Transfer Port 0.169", Valve Port 0.161"; 880 fps, SD 3.7
Barrel Port 0.172", Transfer Port 0.169", Valve Port 0.166"; 884 fps, SD 3.6

With the transfer port drilled to 0.169", the extremely thin wall on the bottom end of the sleeve tended to buckle from the compression load, so stopping at 0.166" would be a better choice.... I think I'll try a poly transfer port if I can find any tubing locally (small town).... 1/4" OD x 3/16" ID, correct?.... 11/64" (0.172") seems to be as big as you can go on the barrel port according to everything I have read.... and I have finally proven that there is indeed a slight improvement (1%) over the 0.166" barrel port I have been using, at least on a high powered .22 cal.... Cool

I continued shooting (another 25 shots) until the velocity dropped below 880 fps (the high in this 25 shot string was 892 fps), which occurred at 55 shots and a pressure of 1400 psi.... I was pleased to find that I can shoot slightly below the regulator pressure without velocity loss.... With an 18 gr. pellet, I'm now getting 886 fps average = 31.4 FPE for 55 shots (plus or minus 6 fps) down to 1400 psi, with an efficiency of 1.24 FPE/cu.in.... Twisted Evil

Colour me pleased.... Clap Clap

I haven't a clue how much it would cost to produce this beast.... Most of the modifications I did were very time consuming.... It will take somebody like yourdaddyjoe to figure out how to streamline the process to make it cost effective.... On the bright side, it looks like a 1400 psi regulator might be able to produce almost identical results.... Wink

Bob

rsterne · Moderator

I tried a slightly larger transfer port today, and actually lost a bit... so I put the gun back the way it was but with the addition of a barrel band that fits over the bonnet of the regulator:

I shot a few rounds to make sure the barrel band didn't open up the group (it didn't).... 3 shots in a single hole at 20 feet indoors.... small squares are 0.1":

I think this gun is developed just about as far as I can go without a different regulator pressure.... With these pellets a 1400 psi regulator would probably work OK, as I can shoot down to that pressure and only lose about 1% in velocity.... Rolling Eyes

Modified 2250 Main Tube mounting a QB79 tank block with integral guage mount for Disco guage
Valve from a Discovery, front end tapered, inside bored out to 0.58", threads shortened to 0.4", valve stem slimmed slightly
Exhaust port on valve milled on 20* angle, corner rounded, drilled to 0.166", transfer port 0.169", barrel port 0.172"
JDS AirMan 13 cu.in. tank with 1600 psi regulator, with custom barrel band
Leapers 3-9 x 40 AO Scope in medium height rings, modified stock, and trigger tune
Discovery hammer spring with custom adjuster c/w integrated threads for degassing tool

18.0 gr. JSB Exact Jumbo Heavy pellets
880 fps average = 31 FPE; SD = 2.6
55 shots (3000 psi fill down to 1400 psi)

I'm very pleased with the results.... gotta love these "Lego" Airguns.... BTW, it weighs 6 lb. 3 oz. ready to go.... Twisted Evil

Bob

sniper · Silver Status Member

some people like restoring old cars. my 72 chevy c-10 has so much body cancer i MUST learn to weld. Crying or Very sad

airguns first! Laughing

lego. i like that. Cool

Jaxom · Senior Member

OR....you can drive it over here, and *I* could do the welding bit.... And then buy more airguns! LOL!!!

yourdaddyjoe · Supporting Member

Bob....

Any increase with that 1600 psi reg?

I am consistently getting 950+ now with the valve mods and the Disco hammer spring in my Wana be Disco 2260 Carbine with the 18" barrel.

That is with the 3000/1800 psi remote tank and bench shooting... Louder than a Mother f*****... even louder than my Disco.

Oh... CR Premier HP's are now borderline too light... It loves Kodiaks and Eungens... Thwack! Just ordered 4 tins of each from Pyramid.

rsterne · Moderator

HI Joe....

I'm still using the 1600 psi reg and 13 cu.in. tank I got from JDS Airman.... The setup I got from you is for the "next" project (2260).... I have some belleville washers coming so that I can play with the regulator pressure.... Cool

I can well believe that you are getting 950s with 14.3 gr on 1800 psi.... I get 965 on my setup with 14.3 gr. and 925 with 15.9 gr.... mind you that's a 24" barrel on 1600 psi.... Wink

I'm actually going to see what I can get with 1400 psi so that I can run a 1.8K burst disc on the downstream side.... I have a Boss Max-flow valve coming to try instead of the Disco valve in my 2260.... Twisted Evil

Bob

rsterne · Moderator

I did some more work on my 22XX PCP rifle.... I bored out the valve a touch more, it's now slightly over 3cc (about 50% bigger than a stock Disco valve).... I also increased the volume between the valve and the gauge port / tank block assembly a bit.... These were just detail improvements before I try the gun with a 2000 psi regulator.... Twisted Evil

In order to have a new baseline, I tested the gun with seven different pellets from 11.9 gr. to 28.7 gr.... at five hammer spring settings from maximum (just shy of coil bind) to 8 turns out.... Each two turns is 1/8" less preload on the Disco hammer spring.... Here are the results (5 shots groups):

The first thing to notice is that with the lighter pellets, there is no significant change in velocity between Max. and 2 turns out.... the additional hammer spring tension just eats up air and makes more noise.... Once you go over 20 gr. pellets you start gaining velocity and energy with that last couple of turns of preload, however.... Wink

The next thing to look at is how drastic you lose efficeincy with that last couple of turns.... The number of shots drops from about 35 at 2 turns out to only about 25 at maximum preload.... At 8 turns out, you can get about 140 shots.... Cool

I did the efficiency measurements as an average over all the pellets.... Generally, heavier pellets are more efficient, especially at higher power levels.... Here is an indication of the average energy at the various hammer preloads:

Maximum: 35.1 FPE over about 25 shots - VERY LOUD
2 turns out: 33.6 FPE over about 35 shots - LOUD
4 turns out: 29.1 FPE over about 45 shots - BETTER
6 turns out: 21.5 FPE over about 70 shots - QUIET
8 turns out: 13.5 FPE over about 140 shots - VERY QUIET

There is another interesting trend, however.... At the lower power levels, there is hardly any difference in the FPE developed by the different pellet weights.... in fact at the 29 FPE level, if you take out the Hobbies, all the pellets have nearly the same punch.... If you had to pick a "best" weight, it would be either the 18 gr. JSB or the 21 gr. Kodiak.... At 2 turns out, the Kodiak develops the most energy (35.9 FPE).... Once you crank it to the maximum, however, the EunJins shine, with 40.2 FPE.... while the Hobbies still have not passed the 30 FPE mark.... All the other pellets pretty much line up by weight in terms of power at maximum hammer spring preload.... Shocked

My conclusions are that with the 1600 psi regulator, the middle weight pellets are the best- the JSB Exact Heavy 18 gr. and the Beeman Kodiak 21 gr.... While you can get more energy with EunJins if you crank up the power, the efficiency at those power levels is very poor.... If you want to crank the power down for plinking, it really doesn't matter what pellet you use.... Rolling Eyes

The maximum power level that makes sense for this gun in it's current configuration is about 32-33 FPE.... ie 3 turns out on the adjuster.... At this setting I was getting 904 fps with JSB 18 gr. Heavies (32.7 FPE) with 40 shots between 900 and 908 fps and a Standard Deviation of just 2.8.... and it only loses about 10 more fps over the next 5 shots.... Dialing it down another 30 fps to 30 FPE will give you about 55 good shots, however.... Shocked

Next tests are planned with an 18 cu.in. tank equipped with a 2000 psi regulator.... Twisted Evil

Bob

rsterne · Moderator

I did the testing at 2000 psi today, using an 18 cu.in. tank (physically the same size as a 9 oz. CO2 tank but rated at 3000 psi).... It was a lot of work refilling the tank between sessions.... it takes about 300 pumps to top it up from 2000 to 3000 psi.... Rolling Eyes

I tested it with the same seven pellets.... but after the first string with the Disco hammer spring I realized it wasn't up to the job of venting 2000 psi so I changed it out to a 1.75" long 0.040" wire spring.... I tested it at just shy of coil bind, and every two turns out from there to 8 turns out, the same as the previous tests.... I again used 5 shot groups, with the following results:

This spring turned out to be a nearly perfect match to the 2000 psi regulator.... It is capable of venting the valve nearly completely with the heavy pellets, and the velocity at maximum and 2 turns out is virtually unchanged with the light pellets.... Once again, the last 2 turns in on the adjuster made little difference in velocity, just made more noise and used up air like it was going out of style (17-20 shots per fill).... Shocked

One thing to notice is that as you back out the adjuster past 3 turns, the velocity starts to drop fast.... and so does the noise.... By the time you are out 8 turns, the gun is so quiet you can actually hear the hammer vibrating against the (closed) valve stem.... At 4 turns out, the performance with this setup is close to the same as the 1600 psi setup at 3 turns out.... but the gun is significantly quieter.... This is a result of the valve opening for a shorter duration at the higher pressure.... The pellet receives a sharp, short kick instead of a longer shove.... and there is less air wasted as the pellet leaves the barrel.... Cool

The efficiency measurements are not great at the lower power setting - they are only an estimate.... but this gun sure eats air when you crank the adjuster to the maximum.... but it does produce over 45 FPE with EunJins.... Here are the average numbers at each hammer preload:

Maximum: 39.5 FPE over about 18 shots - VERY LOUD
2 turns out: 38.5 FPE over about 27 shots - LOUD
4 turns out: 31.2 FPE over about 38 shots - SOMEWHAT MUTED
6 turns out: 19.0 FPE over about 72 shots - VERY QUIET
8 turns out: 6.9 FPE over about 270 shots - EXTREMELY QUIET

Once again, at the lower power levels, there is hardly any difference in the FPE developed by the different weight pellets.... However, at higher power levels, the heavier pellets again produced more energy.... At the lower settings, the "best" wieght was the 21 gr. Kodiak, but once the energy went over 30 FPE the EunJins once again proved more efficient, peaking at 45.1 FPE.... Cool

Although this version is capable of producing nearly 42 FPE with Kodiaks and over 45 FPE with EunJins, it comes at a price.... You can only get about 20 shots at the maximum power levels.... This means that for every shot, you have to pump about 15 times.... I found that pretty tiring, so I think a practical limit is more in the 30-35 FPE range unless you are filling from a SCUBA tank.... On the other hand, if you dial it down to 500 fps with Hobbies you can get the effort down to about 1 pump per shot.... pretty darn efficient.... Wink

In conclusion, the 2000 psi regulator can delivery 40-45 FPE with the ability to dial it down to just 7 FPE with the twist of a screw.... If you are running it anywhere near the maximum, you wouldn't want it on a 13 cu.in. tank.... a 22 cu.in. would probably be the choice.... In the middle ranges (~30 FPE), it is capable of the same performance as the 1600 psi setup but at lower noise levels.... However, you need a larger tank to compensate for the fact that you are only using 1000 psi of air (3000 down to 2000) instead of 1400 psi (3000 down to 1600).... The 18 cu.in. tank delivers almost exactly the same number of shots with the 2000 psi regulator as the 13 cu.in. did down to 1600 psi.... with about the same number of pumps to top it up (250-300).... Shocked

I was planning on testing the gun with a shortened valve stem.... but now that I see that the valve seems to be dumping completely (at maximum hammer spring tension) I don't see the point.... Without going to even higher pressures, I think I have reached a practical limit with this platform.... About the only other thing I can think of that might produce more FPE is increasing the valve volume even more.... such as by using the 2-piece valve design I made for Kinetic_Genius.... or going to .25 cal.... or both.... Twisted Evil

Bob

fishmasterdan · Member

Where do you get the Hammer spring?? I have been searching for hours and have not found a discovery hammer spring to purchase.

rsterne · Moderator

I thought it might be informative to compare the 2000 psi and 1600 psi versions with the power dialed back to where the efficiency is reasonable - about 32 FPE.... and also to test my modified Discovery at the same power levels.... The energy level I picked delivers about 29 FPE with 11.9 gr. Hobbies and about 30.5 FPE with 14.3 gr. JSB Express, peaking at about 32.5 FPE with 21 gr. Kodiaks.... I chose the 18 gr. JSB Heavy for testing.... Here are the results:

The first thing that becomes obvious is that the 2000 psi version is pretty consistent (about a 2% spread) until the tank pressure drops to the 2000 psi regulator setpoint (shot 40).... and then the velocity increases in a classic bell-curve before dropping back to the starting velocity at only 1400 psi (600 psi below the set point).... This shows that if you reduce the power setting significantly below maximum what to expect with a regulated PCP.... The effect would be even more magnified at lower power levels.... Shocked

The 1600 psi regulated version acts the way you would expect a regulated PCP to behave.... As the tank pressure drops, the regulator suffers a slight downward drift in pressure (about 5% ~80 psi), causing the velocity to increase slightly (about 2%).... After the tank drops below the regulator setpoint of 1600 psi (shot 40) the velocity tails off as expected.... This indicates a PCP setup just about perfect.... All regulators will show a slight drift in pressure.... They tend to have slightly higher output pressures at higher tank pressures because the extra pressure holds the regulator open a tiny bit longer.... More expensive regulator designs will tend to be less prone to this, of course.... but for practical purposes, a 2% velocity variation is very good.... Incidently, whether the velocity drifts up, down, or remains steady will depend on exactly where you are on the velocity - pressure bell curve for the pellet - hammer spring tension being used.... Wink

When we look at the Disco, we see a typical unregulated PCP bell-curve.... It is only 15 shots long because, of course, the Disco was designed to deliver about 22 FPE, not 32 FPE, and it has a small reservoir.... The starting pressure was 2000 psi and the pressure at the end of the string was 1400 psi.... It looks pretty curved, but remember, it still only has about a 2% variation in velocity over the string.... it's just that this graph makes it look that way.... Rolling Eyes

How does the efficiency compare?.... The two regulated versions are very close.... The 2000 psi version delivers 1.09 FPE / cu.in. of air used (at STP) while the 1600 psi version delivers 1.04 FPE / cu.in.... The surprise was the Disco, which delivers 1.46 FPE / cu.in of air.... Part of this is because the efficiency of an unregulated PCP is higher on the first half of the bell-curve (when the valve is retaining more air and the pellet is receiving a short, sharp "kick").... You can see this because the pressure loss is a curve, not a straight line like in a regulated setup.... You can also hear it as the gun is quieter in the first half of the string (less wasted air).... Incidently, my modified Disco has actually better efficiency than it had stock (mine was 1.30 with the same pellet).... Shocked

....

I also suspect that the inherent design of this regulated PCP is causing a loss of efficiency because there is very little volume between the regulator and the valve.... My suspicion is that during a shot, without a large volume in this area to replenish the valve, the valve loses more pressure than if a bigger reservoir were present.... This in turn, I believe, lets the valve stay open longer (for a given hammer preload) rather than shutting as quickly as it would if the pressure remained higher.... What I am saying is that I believe that a bigger space between the regulator and the valve would deliver potentially more maximum power (providing the hammer can dump the valve).... and greater efficiency when you are not using that power.... I may incorporate this idea into a follow-up design.... Twisted Evil

Bob

rsterne · Moderator

PM AirGunEric.... he usually has Disco hammer springs in stock....

Bob

fishmasterdan · Member

What an excellent write up. Thank you. Your project has inspired me also.

I am getting similar results as you (a little less FPE). I have been averaging 30 FPE with 18.1 JSB diablo chronied 4' from the end of the barrel.

I really dislike the trigger pull weight I am getting. At 30 FPE it requires a pretty stiff hammer spring (.040). I have tried stock/.035 and .40 wire thickness.

Any tips on improving the trigger? I have polished all surfaces to a shiny burr free surface.

rsterne · Moderator

You can install a lighter sear spring, but don't go too light or the gun won't be safe.... Cock it without a pellet and bang it around (safety off) to make sure it's OK and won't fire accidently.... Rolling Eyes

Bob

packrat · Senior Member

DAAAAAAAAAAMMMMNN !! THAT is what I call a technical report of the first order..I salute you guys that can do stuff like that...amazes me no end!!! I REALLY want one of those 22xx jobs...NOT anywhere as powerful/intense/elaborate as what ya'll are talking about here, but definitely in the 700-750 fps range.. Guess I'll just call Mountain Air and log onto PayPal. Laughing

Thanks for taking the time to post all that stuff...keeps my interest in airgunning maxed out !-Rodger