2240 Velocities - New Extended Valve to fit 2250 Tube !

I decided it was time I did a bit of work on the humble 2240.... I got a new one, took it apart and cleaned it, put on a Crosman steel breech, and an RVA (rear velocity adjuster aka hammer spring preload adjuster), dropped in a CO2 cartridge, and got out the Chrony.... Using the stock 8" barrel I tried five RVA settings; stock, 1 and 2 turns more preload, and then 1 and 2 turns less.... I didn't have enough threads to reduce the preload further.... I then repeated the process with a 14" barrel and a 24" barrel.... All barrels had stock barrel ports, and a stock 0.140" transfer port was used for all the .22 cal testing.... Then I fitted a 24" Lothar Walther barrel in .25 cal (using a poly port) and ran them one more time.... The testing was done shooting only about 1 shot per minute at 67*F, and here are the results....

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When I did the test with the 8" barrel I wondered if I had enough travel, as the velocity was NOT affected at all by the change in preload.... However with the 14" barrel fitted there was a slight drop at 2 turns out, and with the 24" barrel, it was pronounced, nearly 20 fps.... With the .25 cal barrel the velocity started to drop at 1 turn out, and it was down about 20 fps at 2 turns out.... What does this tell you?.... Well, at typical room temperature, the hammer strike in a 2240 is too strong, so it's wasting CO2 for a start, particularly with a stock barrel.... With a 14" barrel, which is capable of using the CO2 more efficiently, the velocity is still on a plateau until the preload is reduced by 1/8", where it is just starting to drop.... It's not until you use a 24" barrel that you reallly start to see a drop in velocity with the preload backed out 1/8".... This is in perfect agreeement with theory, by the way, and if you look at the velocities, you will see that the longer the barrel, the more power, even with a stock valve and porting.... If you modify the gun, that difference will become even more pronounced....

I thought the test with the .25 cal barrel was quite interesting.... First of all, it shows that with a stock 2240 and a 24" barrel, the gun is pretty much shooting at 450 fps with 25. gr. JSB Kings.... In fact, when I tested the gun with 20 gr. H&N FTT's one shot was over 500 fps.... Now if you used a "proper" length pistol barrel, that velocity would drop, of course, but I found it quite surprising that a stock valve and porting could deliver that much power in .25 cal.... In case you're wondering, the gun was returned to non-PAL specs right after the testing....

The fact that the hammer spring preload on a stock 2240 is too great at this temperature means a couple of things.... First of all, that is the reason the 2240 is a gas hog, particulary with the 8" barrel.... Secondly, this likely wouldn't apply at a higher temperature.... If you were shooting on an 80-90*F day, not only would you get more velocity, but the point at which the velocity starts to drop would move to higher preload settings.... However, it also means that by reducing the preload from stock, you can tune the gun to shoot the same velocity at normal temperatures, and the velocity won't increase as much in high temperatures.... If you can accept detuning the gun a bit from it's stock power, you can get to the point where the velocity will actually DECREASE in high temperatures, and NOT DECREASE as much in low temperatures.... This is because the valve can be made to self-regulate just like the way a PCP does....

Next I plan to do some lift measurements to see how far the valve is opening at various RVA settings....

Bob

This morning I got a chance to make some lift measurements on this 2240, which is stock other than a 14" barrel, steel breech, and RVA (PA).... I added a small, light piece of tubing inside the spring, protruding through a hole in the RVA adjusting screw, and carrying an O-ring so that I can measure the lift.... The rod moves with the hammer (it is captured between the inner end of the spring and hammer) and the gap between the O-ring and the end of the adjuster equals the lift of the valve....

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This allows direct measurement of the lift on each shot, all you do is reset it by pushing the O-ring against the adjusting screw before cocking the gun.... The piece of aluminum tubing I used weighs less than 2 grams (~3% of the hammer weight), so has virtually no effect, providing it slides easily through the adjusting screw and the O-ring isn't too snug a fit.... I adjusted the RVA to coil bind, which turns out to be 6 turns in from stock, and measured the velocity and lift at every 2 turns of adjustment, with the following results....

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This is exactly as expected, and although I didn't measure the CO2 use (yet), it should pretty much follow the lift curve.... I'll expend 2 CO2 cartridges, one at maximum preload and the other at stock, recording the shot strings, just to show you how wasteful excessive hammer strike is....

Bob

Here are three shot strings with the same setup as above, a stock 2240 with 14" barrel, RVA, and steel breech.... Pellets were as above, 14.3 gr. JSB Express, with three preload settings, 6 turns in from stock (just shy of coil bind), stock, and 2 turns out from stock (the minimum I can get with this adjuster).... I shot one shot every 30 seconds, and judging by the shot strings, that was a bit too fast, causing cooling that dropped the velocity and shot count.... One shot per minute would be better.... I also weighed the CO2 cartridges before and after and calculated the weight of CO2 in each....

http://i378.photobucket.com/albums/o...ps353ade53.jpg

Your brain can pretty much fill in the two strings I didn't shoot, at 4 and 2 turns in.... Counting all shots above 300 fps they would be about 38 and 43 shots, respectively.... There are a couple of interesting things to note.... At the maximum setting, the first half-dozen shots DID show a bit higher velocity, but they were accompanied by a spray of liquid CO2 that was very visible, as were the first 2-3 shots when the preload was set stock (not as much liquid, but noticable).... I think what is happening is that the dwell is long enough that when the cartridge is full, some of the liquid creeps along the sides of the piercing pin into the valve and is blown out the barrel.... It gives a small boost to the velocity, but is VERY wasteful of CO2.... Interestingly, when the preload was set 2 turns OUT from stock, the first shots didn't show that boost (or spray)....

At maximum preload, the velocity pretty much just keeps dropping with every shot.... After the first 8 shots, the velocity is LESS than what you would get with a stock setup, when shooting every 30 seconds.... On the other hand, with the preload 2 turns (1/8") out from stock, the velocity is much steadier, matching or exceeding the stock setting from shot 4 onwards.... I also calculated the average velocity, average and total FPE, and FPE from every gram of CO2, as follows....

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There appears to ba a slight advantage to using maximum preload, but remember that it is a short string and the first few shots are extracting a bit of extra power from liquid CO2, so it's not as good as it looks.... One glance at the total FPE generated by a single CO2 cartridge really tells the story.... I'll make note of one thing here.... A few years ago I made a 1750 (.177 cal) with an 18" barrel, detuned it to stay right around 500 fps, with a short hammer stroke and light preload, so that the valve was self-regulating from 35*F to 75*F within about 30 fps.... It got over 140 shots totalling over 600 FPE, setting a record for the most FPE from a single CO2 cartridge that AFAIK, still stands today....

Hopefully this information will keep people from trying to get more power from a 22XX by leaning on the hammer spring.... I will say one thing, without a Chrony you would think you had a powerhouse by doing that.... The gun is much louder, and the CO2 spraying out gives the impression of more power.... The results from a short barrel will be even more disappointing....

Bob

I just calculated out an interesting tid-bit of information.... If you expand 12 gr. of CO2 to STP it occupies 400 CI.... So, if the gun makes 400 FPE on a cart., that works out to 1.00 FPE/CI, an interesting way to compare it to HPA....

Bob

I've been thinking about the possibility of an extended valve to fit in a 2250 tube for some time, and the work I did over the last couple of days was to establish a baseline for this experiment.... I was wondering what would happen if I increased the valve volume, and since a 2250 tube is 1.6" longer than a 2240 tube, I simply made a 1.6" long extension to fit in the middle of the valve and lengthened the piercing pin by that amount.... Here are the parts....

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The extension has a small pocket milled in the bottom to miss the front trigger mounting screw.... Above that, back to the valve seat, the extension is drilled 3/8" ID, and in front of that it is drilled 33/64" and the front part is tapped 9/16"-18NF.... The spring seat is just like in the original valve front, except the air passage is 17/64", and the male threads are shortened to 0.30", and the same is done on the valve front (originally they were 0.50" long).... These changes basically triple the volume inside the valve to about 5 cc.... The piercing pin was also lengthened 1.6" with a pointed piece of 1/8" piano wire, joined to the old pin (which was ground flat on the end) with a sleeve of 1/8" ID brass hobby tubing 1" long and glued in place with shaft retainer.... Here is the assembled valve....

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The original spring was used, and the original poppet (except for the longer piercing pin).... plus 2 of the original size O-rings.... The valve just drops into the 2250 tube and is secured by the single 6-40 screw on the bottom as per the original setup.... You simply drop in a CO2 cartridge and use the original 2240 CO2 cap to hold it in place.... Cock the gun and fire it to pierce the cartridge, exactly as per the original....

Before disassembling the gun to fit the new valve in a 2250 tube, I installed a new RVA.... I got a Crosman power adjuster from the Challenger, which uses a 24 TPI screw instead of the 16 TPI one I had.... In addition, it has longer travel, and I lengthened it even more by drilling out 3/16" of the threads on the inside to allow the hammer spring to move back further.... It now has 18 turns of travel (3/4") from coil bind to the minimum setting.... Since the adjuster was new, I did a few tests to correlate the previous information to the positions of the new adjuster, then stripped the parts out of the 2240 tube and reassembled them into the 2250 tube, but using the extended valve.... I dropped in a new cartridge and started testing by checking to see not only if and how much the velocity changed, but how that change related to the new RVA.... Here is the results of that initial testing....

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The black line is the 2240 with the original valve, and you can see that 12 turns out is where the velocity starts to decline, above that it plateaus.... With the new, extended valve (blue line), the plateau is moved 3 turns to the left (more preload), and the exciting part is that the velocity increased 55 fps.... That is an 11% increase in velocity and a 23% increase in FPE - JUST from the new valve, with no other changes.... In .25 cal, the difference is even greater.... The plateau also shifted 3 turns to the left, and the velocity increased 65 fps (15%), increasing the FPE by 31%.... That's a BIG increase in power from just increasing the valve volume.... I was hoping to see an increase, but I'm overjoyed to see it so dramatic.... Now it was time to shoot a string with the .25 cal and see what I got.... I loaded a new cartridge, shot three shots just to confirm the velocity results at 3, 5, and 7 turns out on the preload, set the adjuster to 9 turns out, and shot one shot per minute until the velocity dropped to 300 fps....

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You can see the first three shots, mirroring the velocities in the above graph, and then the string at 9 turns out beginning on shot #4.... One thing became obvious during this, and the first cartridge I shot using the new valve, and that was how stable the velocity was.... Admittedly, part of the level shot string is from shooting every 60 seconds instead of every 30, but there is no question that the larger valve not only increased the performance a lot, but decreased the shot-to-shot variation as well.... Including all 28 shots, the average velocity was 466 fps (12.35 FPE), extracting 28.1 FPE from each gram of CO2 (nearly as good as the best results yesterday in .22 cal) and the efficiency worked out to 0.84 FPE/CI.... If you looked at only shots 4 - 23 (ie 20 shots), the average was 476 fps (12.8 FPE) with only a 19 fpe ES (4%).... and the efficiency would have been higher as well....

I'm extremely pleased with these results.... I've never seen anyone make a valve extension to stretch a 22XX valve to fit into a 2250 tube before, and when you consider the big improvement in performance WITH OTHERWISE STOCK VALVE AND PORTING, this may have the potential to unleash more performance on CO2 when combined with other modifications.... The idea I had, which seems to have been proven, was that by using a larger valve, the pressure drop inside the valve during the shot will be less, increasing the AVERAGE pressure during the shot cycle.... The fact that more preload was required to reach the velocity plateau is proof that indeed that happened.... The piercing pin nearly blocks the inlet to the valve completely, so all we have to work with is the volume inside the valve.... The only other alternative is to go to a bulk fill arrangement and increase the diameter of the valve inlet, but that brings another set of problems.... the major one being that if you raise the muzzle on a bulk fill gun, the valve fills with liquid CO2, resulting in inconsistent velocities and a horrendous increase in CO2 consumption as the cloud of liquid blows out the barrel.... If you stored this gun with the muzzle up, I suppose this could happen, but the clearance between the piercing pin and the hole in the valve front is so small that it would take a while.... I think this is an excellent way to get (nearly?) bulk-fill performance and still be able to use the 12 gr. cartridges....

The fact that the .25 cal responded even more to the extended valve than the .22 cal makes perfect sense.... The bore volume (for the same barrel length) is 33 % greater, so it NEEDS a bigger valve anyway.... In fact, I hope to be able to use this greatly increased valve size to experiment with even larger calibers, building a 3050 and maybe even a 3550.... I wonder how large I can go on caliber and still get a pistol that shoots over 400 fps on CO2 ?.... Sean and I have the barrels available, in .300 cal and .357, designed for the new JSB pellets.... The 25" rifle barrels are just begging to be cut in half and tried on a CO2 pistol with the new extended valve....

Bob

After measuring the lift in stock form, and finding out it was TINY, I thought about what was happening inside a stock 2240.... The hammer is VERY heavy for the FPE level of the gun, and the hammer spring is very weak, leading to small lift and long dwell.... In a PCP, this tends to be inefficient, so I decided to make an extreme change as an experiment, and lightened the hammer by 50%, from 60 gr. to 30 gr.... I turned down the middle of the hammer to 3/8", leaving only a small portion at each end that was full diameter.... You have to grind through the case-hardening to get even a carbide bit to bite, but once you are down about 0.030" you can turn it down OK, as long as you are working from the inside out (ie softer core to the harder outside layer)....

I tested the velocity and lift once more with the stock hammer, graphing both vs. the preload over a range that spanned the "knee" of the curve, to show both the plateau on the left and the downslope on the right.... I then swapped out the hammer, and repeated the test with the light one.... The results were as expected, a big drop in velocity for any given preload because the lighter hammer, while having the same energy, has only 71% of the momentum (square root of the weight at 0.50), so that means only 71% of the dwell, while maintaining the same lift.... This means that to reach the plateau you have to increase the preload, adding energy until that balances the loss in dwell.... It turned out that even at maximum preload (ie coil bind) I could not quite reach the original velocity, although you could just see the beginning of the plateau.... I then tried a 1377 hammer spring, and then settled on one from a Disco for the next test.... I repeated the test, achieving the highest velocity to date in .25 cal (528 fps) with a clear plateau, knee, and downslope.... Here are the results....

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You can see that with the light hammer and the Disco spring, the plateau (maximum velocity reached) was about 10 fps more than the previous best.... I think that is because the valve is opening more quickly, so that the initial "pulse" of CO2 arrives quicker, and the pellet gets a bit more acceleration in that critical first part of its travel.... The lift was much greater with the Disco spring, and that alarmed me that it might mean a lot more CO2 might be used, so I set the gun up for the same velocity as the string I shot yesterday (starting at 500 fps, averaging about 465), and I actually picked up 4 shots, so the efficiency is actually higher.... The report sounded different today, it was louder, but more of a sharp POP and less of a BURRRP, so I think the gain in efficiency may well be less hammer bounce due to the shorter, stiffer spring.... Whatever the cause, I'll take it !!!

This gun is already over PAL velocities, and if I were planning a rifle, I could use a 2260 tube and clip the hammer spring to keep it just under 500 fps.... In other words, I have already achieved a .25 cal CO2 non-PAL rifle, with basically just the valve extension (the lighter hammer was just icing on the cake).... However, I want to use a pistol length barrel, and my calculations show that with half the barrel length, I would only get about 400 fps.... Therefore, I'm going to modify the porting in the valve to (hopefully) increase the power so that when I step down in barrel length I will be in the high 400s.... I figure I need to get closer to 600 fps with the 24" barrel to achieve that goal....

Bob

I pulled the valve out today and drilled out the ports.... The throat is now 0.250" (still a stock valve stem, so 0.195" equivalent), the exhaust port is 0.211" (done with a 3/16" mill angled 20*), the transfer port is 0.219", and the barrel port is 0.190 x 0.250" (0.220" equivalent).... The transfer port is 5/16" OD Teflon rod, so I had to drill the breech and main tube to that diameter.... Otherwise, the gun is the way it was yesterday, lightweight hammer and Disco spring, Extended Valve with about triple the original volume, and the power adjuster from a Challenger, all mounted in a 2250 tube.... The barrel is a 23.8" Lothar Walther with a 12mm OD, turned down to fit the Crosman steel breech.... The first cartridge was used to test the velocity vs. the preload, and then I installed a new cartridge, set the preload to 6 turns out, and shot a string using 25.4 gr. JSB Kings.... Here are the results....

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The red line is the results from yesterday, same gun with stock ports, and the black line is today with the bigger ports.... As you can see, I picked up about 75 fps, reaching 603 fps (20.5 FPE), and the knee of the curve shifted one more turn to the left.... so the plateau now starts a couple of turns from coil bind on the Disco spring.... One thing interesting to note is that at lower preload settings, I'm getting more lift on the valve (ie a flatter lift to preload curve).... I think this is a result of the larger throat decreasing the pressure differential across the head of the poppet, and allowing the valve to open further, increasing both the lift and dwell.... I did a small amount of streamlining on the head of the poppet near the valve spring seat, so is also possible that reduced the drag which was reducing the lift.... It shows what happens when you make more than one change, it becomes impossible to determine what causes the results to change....

I once again shot one shot per minute, and at this higher CO2 use that is not enough time between shots.... The velocity is pretty much a linear decline throughout the string, and the gun got progressively colder with each shot.... It would be interesting to shoot another string, waiting like 5 minutes between shots, I'm betting a lot more energy could be extracted from the cartridge.... As it is, I averaged 528 fps (15.9 FPE) over the entire 23 shots which were above 300 fps, with an efficiency of 0.88 FPE/CI, nearly as high as at the 12 FPE level with the stock ports.... The 19 shots which were over 500 fps averaged 549 fps and 17 FPE.... Thats a lot of power from a 22XX platform running on a 12 gr. cartridge.... I'm pretty sure that when I get a 12" barrel I should be able to tune this gun into the high 400s, setting it up as a good non-PAL .25 cal pistol on CO2....

Bob