Back when I was testing the Custom Cr2240 (friend's pistol) I also found that velocity dropped continuously when I had no rest break. Velocity was more consistent with a one minute rest between shots. I managed 540fps with the 12" barrel at 69F temp. I think output would have been better once I fixed the breech seal. Crosman 14.3gr WC did 534fps when the breech seal was working best. The shot count with this pistol was only 22-24 which was poor. I would rather give up some velocity to get another 10 shots.
That sounds very good 14.3gr. at 534.
I've done before using 2289 hammer spring and that causes velocity to drop so fast with short time between shots. Too much co2 cools off the valve & port and the 12gr. powerlet but won't effect with 9oz or larger.
I've done 7" barrel at 525 with hobby pellet, what I would like to achieve is 7" barrel at about 540 to 550, just with port mod. may be not possible with co2 powerlet.
The Custom 12" CR2240 that I tested had lots of valve work done. A guy out in Alberta (WhiteWolf-Kim Kowalchuk) tuned it for my friend about 4 years ago. It had heavier hammer spring, lighter valve return spring, enhanced valve capacity, stem mods, port angle. As I mentioned, it only got about 23 shots per powerlet. Good power but no economy. Yep, your tongue would likely stick to the pistol after shooting 23 shots quickly
A few years ago ShaggyCanuck (Trevor from Alberta) did some tuning with his Cr2240 with 7" barrel. He managed 455fps with 14.3gr Crosman WCs. By using the energy output (6.58FPE) I estimate the output with 11.9gr Hobby to be about 499fps.... assuming constant FPE. I'll post his results, from an old e-mail, if I can find it.
Modified Crosman 2240 with 7" factory barrel. Time between shots was 1 minute and temperature was 20C. Distance was 8-10ft from chrony. Test done with 14.3 copperhead pointed pellets and Brass Eagle powerlets.
dnr = did not register
1st string (adjustable end cap set to stock hammer spring preload)
453.0, 449.4, 450.3, dnr, 454.5, dnr, 453.0, 449.1, 448.8, 449.6, 450.1,
449.6, 453.2, 449.4, 438.8, 446.3, 448.4, 447.3, 443.3, 438.1, 443.4, 442.3, 439.4, 440.7, 437.5, 433.4, 421.3, 409.9....
powerlet contained 176grains co2
4th string (stock end cap, hammer spring shortened 0.045" approx. 1/2 coil cut off and then reshaped)
453.7, 454.9, 454.3, 443.8, 452.1, dnr, 453.7, 458.1, 454.9, 459.8, 460.9,
461.4, 460.9, 464.6, 462.4, 464.3, 532.7, 465.0, 458.3, 458.6, 461.2, 457.8, 460.8, 461.6, 461.9, 526.7, 516.2, 458.5, 535.4, 456.9, 455.9, 517.3, 446.9, 441.3, dnr, 421.5.... the furnace was bound to come on sometime. temp increased to 21C during this string. powerlet contained 174.5grains co2
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I did some number crunching for Trevor's Cr2240 results for comparison purposes. It almost appears that ALL the settings were almost the same for average velocities. Maybe up or down 50 thou on the end cap doesn't really make much difference in the long run.
I averaged the velocity for the first 20 usable shots for each string. This
eliminated only 2 shots from the first 22 from each string. Each string has
2 dnrs or highvel shots so I did not use them. The first 20-22 shots would
be good for hunting because they are all decent in velocity.
Here are the average velocities:
The 4th string might have been a bit lower if the furnace did not turn on.
I also did a shot count for all shots over 438fps for each string. Here are
the results:
The 4th string could be a result of more pressure because of increased
temperature from the furnace. This string could be done over with 20C temp.
All in all, you can see the first 3 strings are very close for average
velocites and shot counts. The 3rd string looks a bit more attractive with
the two factors (shots/ave vel) taken into consideration. Giving a definite
preference is not possible because the data is so close.
The pistol is getting a bit over 6ftlbs of muzzle energy.
Hi Todd,
I just re-run another test with the same 2240 but this time with crosman 14.3 gr. Dome pellets.
15 seconds max between the shots. I use a stop watch.
I think the best is not to touch the valve or hammer spring. Next Friday if I got more time, I will get another 2240 and run more experiment but this time with 7" barrel only, perhaps with cr steel breech or cb breech that I still have some in stock.
I think, we should be able to get 500 to 510 with 14.3 gr. with 7" barrel without modifying spring hammer or valve. Maximize the use of the co2 power by modding the port to the max. you get the best perf. 2240 and value for the money at the same time really good for hunting power and in case of cold weather, still have some juice left.
i have no hassel with the copper or alumin' . i can never seem to find 1/4'' poly tube so i use what ever .
what ever i use works well . to test it i pulg the barrel tight and fire the gun (no pellet)and see how long it takes the air to seep out . same with springers . if all is sealed good the air should just pressureize and slowy leak off . . (no oils that desil in the springer!)
Do you think there is that much wasted power at the port? As was tested, the unaltered 2240 does approx 416fps with 14.3gr Crosman WCs at room temp. Getting another 90fps from only improving the seal between barrel and breech would be sweet. Are you planning on increasing port size or just improving the seal at this junction?
The BRNO TAU-7 and Mac-1 LD Pistol are both good performers in cool weather. Mac-1 web site shows very little velocity change from 45F to 65F. There is a slight increase in velocity at 85F but it drops again at 95F to the same as when at 45F-65F. Approx 10% change in velocity from 45F to 95F.
When I tested my TAU-7 I had no change in velocity at 55F and 70F. I used a thermometer when reducing room temperature by shutting off the heat in my testing room during winter months. I used the same fill for all temperature testing (on my web site). At 80F I would see an increase in velocity by 6%-8%. I did not test down to 45F or up to 95F, like Mac-1 did.
The TAU-7 and LD pistol have a common item in design. They both use very light valve return springs and moderate tension hammer springs. The TAU spring can easily be compressed between your fingers, like a ballpoint pen spring. There is a purpose to this design and it seems to work. As Tim says "Valve duration is balanced w/ pressure by passing low volumes of high pressure or high volumes of low pressure to yield a nearly flat performance across the pressure spectrum."
The other common design trait for the TAU and LD is the vertical CO2 reservoir. This apparently prevents liquid from approaching the valve. A Cr2240 with bulk and remote line should do the same, I would think.
There is a problem with going too light on the Cr2240 valve return spring. With a moderate hammer tension the powerlet might puncture but a weak return spring will sometimes allow the pin to stick in the powerlet when pressure drops real low. I have seen this happen a couple of times with the customized pistol that I tested, but it's was not a common occurence. It's best to dump the powerlet as soon as the shot sound indicates pressure is dropping fast. With bulk, the pin can be chopped off to eliminate the potential problem and possibly create a less sensitive pistol with a lighter return spring and slightly lighter hammer spring (balanced for velocity).
I am only throwing out ideas for Cr2240 improvements. I make no claims to be very knowledgable in this area.
Do you think there is that much wasted power at the port? As was tested, the unaltered 2240 does approx 416fps with 14.3gr Crosman WCs at room temp. Getting another 90fps from only improving the seal between barrel and breech would be sweet. Are you planning on increasing port size or just improving the seal at this junction?
Yes, there is quite a bit of co2 is not use at the port. That's a good thought for an experiment, not just increasing the port size but also improve the seal ...... hmmmm.... I just got an idea ......
