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rsterne · Moderator

HI Broom....

Think of the total FPE as a measure of the efficiency of the platform.... the amount you are actually GETTING out of a 12 gram cartridge compared to what it is capable of.... (SinNC says that is theoretically 700 FPE, but I have no idea where he gets that number from).... If that is true, using the self-regulating "Low Power 8" setting, I am getting about 78% efficiency over the usuable part of the shot curve.... and about 82% down to 300 fps.... That would be a valid comparison to SinNC's .22 cal chart (in the previous link) where he gets 515.6 FPE / 700 = 74%.... Wink

Bear in mind that the more velocity you reach for, the lower your efficiency will be, and also shorter barrels will hurt.... In both cases, you are losing more gas "after the train has left the station" which shows up as report (noise).... There are two settings I am particularly interested in.... "High Power 4" which produced more average velocity and a flatter shot string than "wide open" and 60% more shots.... and "Low Power 8" where the gun is self-regulating over a pretty decent temperature range (only more testing will prove how wide that range is).... Cool

Bob

ustilago · Member

So uh, Bob. . . how many cartridges have you gone through so far? And how many do you have left from your big order?

One thing you might also consider, I noticed this with Crosman cartridges, Are you really getting 12g per cart?
I weighed the last box of 40 I picked up from Elbonian tire and wrote the weights on the carts in black Sharpie. Once I'm done with the carts, I toss them in another box and I'll weigh them empty when I have a few minutes (and a pile of empties). You might be surprised at how inconsistent they can be Shocked

so far, out of this box I've had one dud (totally empty) and one with only 2g of CO2.

Just one more variable. . .

broommaster2000 · Moderator

I can recommend any CO2 gunner to bulk fill. There are a lot of nice kind of BF's these days,

rsterne · Moderator

I wandered over to the one "Machine Shop" in Princeton yesterday on the off chance he might have some brass scraps.... and lucked out.... he had a small piece of 1/4" brass plate and 8+ inches of 7/8" Brass Hex.... perfect for a 2250 front grip mount and a Muzzle Brake / Barrel Stabilizer.... Most of the day with the lathe and mill and then some polishing and TADA.... Wink

The Brake / Stabilizer ended up weighing just over 7 oz.... should give me a bit of mass to help when shooting offhand....

The beautiful barrel band I bought from ustilago was for a 2240/60 and didn't have a mount for the front grip.... I machined one up with a radius to match the barrel band and a shoulder to keep it from rotating.... the only tricky bit was getting the bolt the right length so that the mount was tight at the same time as the band tightened on the tube.... a shakeproof washer gave me a bit of fiddle room.... I understand usti will eventually be offering a (one piece?) barrel band c/w mount for the 2250.... Cool

Bob

jonathan · Member

Looks great.....cant wait to see them on the monster!!!

broommaster2000 · Moderator

Shiney! I've always liked the brass look over chrome on an airgun. Exclamation

rsterne · Moderator

I tried a stiffer spring in the valve.... a cut-down 2289 valve spring.... It wasn't a huge amount stiffer, just longer so more preload....

What I suspected might happen did prove to be the case.... The velocity dropped at equal power settings.... a LOT on the "economy" settings.... I could no longer get 500 fps on low power, the best I did on Low Power 10 was a 455 average (427 low, 474 high).... worse spread than before.... On Low Power 8 (where I used to get 500 fps) I was getting only 421 average (412 low, 436 high).... all were 10 shot strings.... The velocity didn't change much on the High Power settings, but was slightly lower.... and no more consistent....

I then tried a weaker spring in the valve (from a 2289 valve with the long check).... it was 0.036" wire instead of 0.042" and slightly longer.... When I just started assembly, I noticed that the hammer was opening the valve with the adjuster about 2 turns from coil bound on the hammer spring (ie Power 8).... I never bothered finishing the assembly.... just put it back to a stock internal spring....

I checked that nothing had changed, and then drilled the barrel port out from 0.136" to 0.144" (ie #27 drill), which is one size larger than a stock transfer port.... The plan was to alternate drilling the barrel port and transfer port, going one numbered drill size larger until I lost performance.... then I could back up one size since I had a spare stock transfer port.... I definitely picked up some velocity, so I drilled the transfer port out from the stock 0.140" to 0.0147" (#26 drill) and promptly lost about half of what I had gained.... Shocked

It would appear that with my 18" .177 barrel, the stock transfer port is perfect, but the barrel port benefits from being enlarged to one size larger than the TP.... Full numbers to follow....

Bob

rsterne · Moderator

I have always wondered just how much effect temperature had on CO2 performance.... and how the Dual Power Hammer might be tuned to eliminate or reduce this effect.... During the testing so far, I have learned just how drastic the effect of continuous shooting is on velocity, and have learned to allow the gun to come back to ambient temperature between shots.... Rapid fire and CO2 just do NOT go together.... Rolling Eyes

My procedure for testing is to shoot, write down the velocity, load the gun and cock it, and then place my hand on the side of the tube where the valve and CO2 cartridge is to allow some of the heat of my hand to flow back into the cold gun for the same time between shots.... varying the time depending on the DPH setting.... More time is required for higher velocities because more cooling occurs on each shot.... Typically, I allow about 45 seconds between shots on high power, and about 30 seconds between shots on low power settings (developed purely through experience by watching the way the velocity deteriorates if I don't wait long enough, YMMV).... Once I find a good "time between shots", I use it for the entire shot string.... Interestingly, when I find the "sweet spot" on the DPH that is basically self-regulating (ie temperature independant), I can actually prove it by rapid-fire shooting alternating with "over-warming" the gun.... when the hammer is just right, the velocity readings basically don't change because of the self-regulating nature of the spring balance.... Since developing a consistent (and patient) shooting technique, the shot-to-shot variation is much less.... Cool

The following graph shows six shot strings, all with the DPH hammer set at Power Level 9 (ie about 1.5 turns from coil bind), as this is the closest I can get to self-regulating on Low Power.... You can see just how close the velocity is from 46*F to 75*F and from the beginning of the string to the end when using "Low Power 9".... Note that the velocity at 75*F is actually slightly LESS than at the lower temperatures (ie the self regulation is not perfect).... Compare this with the performance on "High Power 9".... The shot strings fall from initial shots to the end of the useful range, and the velocity drops about 50 fps from 75*F to 62*F and another 50 fps when you get to 46*F.... which is typical performance of CO2 (without self-regulation).... Rolling Eyes

Here are the actual numbers:

High Power 9:
75*F - 666 fps avg, 690 high, 638 low over 31 shots, 301 FPE total (down to 300 fps)
60*F - 613 fps avg, 639 high, 589 low over 32 shots, 245 FPE total (down to 300 fps)
46*F - 562 fps avg, 590 high, 545 low over 36 shots, 237 FPE total (down to 300 fps)

Low Power 9:
75*F - 507 fps avg, 529 high, 491 low over 130 shots, 609 FPE total (down to 300 fps)
60*F - 527 fps avg, 539 high, 502 low over 102 shots, 528 FPE total (down to 300 fps)
46*F - 524 fps avg, 537 high, 502 low over 89 shots, 456 FPE total (down to 300 fps)

My conclusions are:

At high power:
There is wide variation in performance over this temperature range....
The shot count is low (because of a lot of wasted gas).... As established previously, this can be improved by over 50% with no loss in performance by using "High Power 4"....

At low power:
The variation in performance over this temperature range is minimal, with careful balancing (in this case, Low Power 9)....
The gun is very economical to shoot, and the use of "Low Power 8" at 60*F and 46*F (from previous testing) would reduce velocities to about the same as "Low Power 9" at 75*F (~500 fps), increasing shot count and total FPEs at the lower temperatures even further....

The total energy developed from a CO2 cartridge is not a constant (~700 FPE is often quoted), but is dependant on the temperature.... Higher temperatures allow more total energy to be released.... resulting in either higher velocities or higher shot count, depending on how the gun is tuned.... Not a revelation, just that I supported the theory with facts.... Rolling Eyes

It is possible, through balancing the hammer spring with the valve spring, to achieve a large degree of self-regulation in the 22XX CO2 platform.... Although you will give up maximum velocity to achieve this, over 600 FPE can be extracted from a single 12 gram CO2 cartridge.... YMMV of course.... Cool

I would highly recommend ustilago's DPH to anyone wishing to improve the efficiency of their 22XX platform.... Whether you want the maximum power with an extended shot count, or real economy at practical velocities for target practice or plinking, it is the route to go.... Twisted Evil

Bob

vAgRaNt · Member

~130+ shots from a cart - Wow!

I really need to find the time to cut down a barrel.

Just as a notation to your post, my similarly equipped (DPH'ed) 22XX gun sporting a 24" .177 barrel, can only pull ~105 - 110 shots @ ~500fps from a typical cart (~460FPE/Cart).

Your experiments conclusively prove (to me at least) that ~18" is significantly more efficient than 24" at the more sedate velocities.

It's got me wondering what the "optimal" length really is. . . . .

Thanks Bob: as usual, excellent documentation!

rsterne · Moderator

rsterne · Moderator

I just thought I'd post a photo of the completed gun.... I have customized the stock and added a Fitco 2-7x32AO scope and mounts I had kicking around, plus my barrel stabilizer....

Shoots as good as it looks too.... Twisted Evil

Bob

rsterne · Moderator

I finally got a couple of 22XX hammers in to use to check out my Rear Velocity Adjusters.... I reduced the diameter in the center of one of them to 3/8" for a length of 0.8" to reduce the weight by 50% from 60 gr. to 30 gr.... I started with the stock hammer and a stock 22XX hammer spring (the valve is stock).... The adjuster was able to be adjusted in until I got coil bind, and had 8 turns of adjustment out from there (1/2").... I did measurements every 2 turns (ie every 1/8" of adjustment), using my 1750 with 18" barrel, with the following results:

From almost coil bind down to 6 turns out, there was no significant difference in the ~670 fps peak velocity (ie with a fresh cartridge, or after allowing the gun to warm to the ambient temperature of 68*F), only the report, which got quieter as I reduced the spring tension.... At 8 turns out, the peak velocity dropped about 30 fps.... I then checked the shot count, with 1 shot every 25-30 seconds, recording only the range of some of the five shot strings:

Almost at coil bind:

shots 10-15: 648 - 630 fps
shots 20-25: 607 - 595 fps
shots 26-30: 596 - 587 fps
shots 31-35: 587 - 516 fps
shots 36-39: 488 - 308 fps

6 turns out:

shots 10-15: 655 - 635 fps
shots 20-25: 629 - 625 fps
shots 26-30: 618 - 612 fps
shots 31-35: 617 - 609 fps
shots 36-40: 611 - 607 fps
shots 41-45: 605 - 574 fps
shots 46-50: 552 - 464 fps
shots 51-53: 434 - 371 fps

As you can see, reducing the spring tension actually increased the average velocity (remember, there was some cooling effect, as I was shooting about every 30 seconds).... and extends the number of usuable shots from about 30 to about 44.... nearly a 50% increase.... I estimated the "stock" spring tension without my adjuster as being about the same as 2 turns out from coil bound.... With the stock spring and hammer, my "velocity adjuster" is more of a "gas economy adjuster".... I was able to get better performance with much less CO2 being wasted....

I then put in a 2289 hammer spring.... There was a slight increase in peak velocity (about 10 fps) with a fresh cartridge, but over the life of the cartridge the performance was virtually identical to the stock 2240 spring.... In addition, I was not able to reduce the velocity, even at 8 turns out.... Changing the spring for a heavier one did NOT improve the performance in .177 cal with an 18" barrel....

I then put in the lighter hammer, but with the stock spring again.... The peak velocity near coil bind was virtually unchanged, although I thought that the report was somewhat less (possibly like the stock hammer at 2 turns out).... When I started reducing the spring tension I found that it had significantly more effect on the velocity with the lighter hammer.... 2 turns out performed about the same as 4 turns out with the heavier hammer.... and at 4 turns out, the velocity was just starting to drop (about 640 fps).... At 6 turns out, the velocity was down to just over 600 fps.... and at 8 turns out it was down to about 560 fps.... The lighter hammer did exactly what I thought it would.... it didn't change much at the top end, but it reduced the velocity at lower spring tensions.... making the adjuster work over a wider range....

The next step was to shorten the spring to reduce the preload even more.... I cut 3 coils off the spring (~ 3/8") and found that with the adjuster in all the way (what used to be nearly coil bound) the peak velocity was still virtually unchanged (665 fps).... The report was much like it was with the original setup at 6 turns out, which makes sense.... The velocity adjuster started to work right away, however.... At 2 turns out it was down to about 620 fps.... at 4 turns out it was about 570 fps.... at 5 turns out about 520 fps.... at 6 turns out about 400 fps.... at 7 turns out, the pellet barely cleared the barrel.... Shocked

.... I tried a 2289 spring shortened about 1/2", and got virtually exactly the same results....

The summarize the results in my 1750 with 18" barrel:

With a stock hammer spring and hammer, the "velocity adjuster" is more useful for tuning the gun to conserve CO2 without losing significant velocity.... you can get a flatter shot string and about 50% more shots per cartridge....

Replacing the hammer spring with a heavier one is a waste of time, and gas, at least in .177 cal....

By replacing the hammer with one 50% lighter, the "velocity adjuster" begins to work the way it should....

It's easier and cheaper to get a wider range of adjustment by simply shortening the stock hammer spring about 3 coils.... I didn't try it with a stock weight hammer, but by playing with the spring length, you could adjust the range from the "self regulating" range (like I did with ustilago's DPH) to maximum but with good economy....

All this is fine, except for one thing.... Once you back out the spring tension about 8 turns (with a stock spring) it won't reliably pierce the cartridge.... Rolling Eyes

.... It goes without saying that shortening the spring will only make matters worse.... Fortunately there was a very simple solution.... I drilled a 9/64" hole through the adjusting screw.... I took a piece of 1/8" steel rod and cut a piece 3" long and deburred the ends.... This will fit down inside the adjuster and spring, and come to rest inside the hammer, with about 1/8" sticking out.... You load a cartridge, cock the gun and fire it.... if it doesn't pierce the cartridge, you insert the rod until it is resting on the hammer.... pull the trigger, and tap on the end of the rod.... this drives the valve open and pierces the cartridge.... You don't need to wail on it, just a light tap.... If you didn't tap hard enough to pierce the cartridge, tap a little harder.... Wink

So I made a bunch of these velocity adjusters and have some for sale.... What do I think of them?.... They will defintely allow you to tune the gun to be more economical without losing performance (pay for themselves in short order!).... If you want to experiment with a "self-regulating" setup (where temperature doesn't affect the albeit reduced velocity, and you get incredible economy), they will work fine for that as well, but you may have to pierce the cartridge manually....

I put ustilago's DPH back in my gun.... It's more expensive, but you can use the "high power" setting to pierce the cartridge.... and you have that instant "kill shot" available by just cocking to the second notch.... On low power, you can tune the velocity to virtually anything you want, and be rewarded with increased economy for the lower velocities.... You can also experiment with a "self-regulating" setup if you want.... Totally worth the money, IMHO.... Twisted Evil

Bob

RatcatcherDino · Member

rsterne · Moderator

The hammer has two cocking positions.... high and low power.... In addition, the adjuster has about 10 useful turns of travel to adjust spring preload.... Wink

Bob