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....



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