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....
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
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