I've been busy with other projects, but figured I better drag out the Hayabusa and do some more work on it, based on what I have learned over the past few months.... I pulled the back end of the gun apart, drilled out the hammer to 3/8" ID, drilled out the RVA, and fitted the hammer spring from a QB.... I now have plenty of spring power so I have lots of adjustment instead of running out of room on the RVA with the shorter springs I had been using previously.... The gun doesn't have any more power with the lighter pellets, but it did pick up a bit with the heavier ones.... I'm still running the gun regulated at ~1900 psi, and here are the results at various hammer spring settings....
I'm now up to 73 FPE with the EunJin Points, and over 60 FPE with the JSB Kings, at maximum power.... However, the gun set up that way is an Air Hog.... I can dial it down 4 full turns on the RVA without losing any velocity and double the shot count, still at 60 FPE with the Kings and 62 FPE with the Baracudas.... Set that way, I would get about 25 shots per fill.... Once again, I found that giving up just a few fps below the plateau works wonders with the air consumption, however.... Backed out one more turn, I only lost 30 fps, and gained another 10 shots or so.... You can see the effect on the Efficiency that the RVA has using the dotted line on the graph above....
This setting (5 turns out on the RVA) formed the basis for additional tests, starting from 1004 fps and an efficiency of 0.96 FPE/CI with the JSB Kings.... The first thing I did was started restricting the transfer port with the adjusting screw on the side of the breech.... You can see the results in the dashed line on the graph.... The first two turns made no difference, I assume because the small protrusion of the ball shaped end on the screw, although restricting the port, was smoothing the flow compared to when it was fully retracted.... At 3 turns in, the velocity dropped to 962 fps and the efficiency jumped to 1.19 FPE/CI.... At that point, I'm getting over 50 shots at 52 FPE per fill, and I can shoot down to 1500 psi before the velocity drops below 950 fps.... Once I get a chance to do some accuracy testing at longer ranges, I can adjust the velocity from 1000 fps down to as low as 600 fps by simply turning a screw in the side of the breech....
When I made the hammer for this gun, I made the throw (hammer travel) adjustable using the adjusting screw from an MRod.... You reach it from the back with a long allen key, by removing the RVA adjusting screw.... With the spring preload at 5 turns out, there is very little static preload on the hammer spring.... As you lengthen the nose of the hammer by turning in the adjusting screw, you reduce the distance the hammer travels, reducing it's momentum.... However, you increase the static preload on the hammer spring because the resting position of the hammer moves back.... These two effects cancel each other out (at the spring preload tested) for about the first 4 turns on the throw adjuster.... and the velocity stays constant.... I did notice, however, that the first shot in the string had a slightly lower velocity, and that difference increased as I reduced the hammer travel (and increased the spring preload).... As I further decreased the hammer travel, the velocity did begin to drop.... By the time I moved the adjustment 10 turns (0.42"), the velocity had dropped to 920 fps, but the first shot was under 900 fps.... I did not check how the efficiency changed as I adjusted the hammer throw, because the inconcsistency of the first shot bothered me.... I ended up backing up the adjuster to go back to the full hammer travel I started with....
My base settings are: Full hammer travel.... 5 turns out on the RVA.... and 3 turns in on the Velocity Adjuster.... That has me sitting at an Efficiency of 1.19 FPE/CI (13.8 Barcc/FPE) giving 50 shots at 52 FPE (962 fps) with the JSB Kings.... With 1 turn on the velocity adjuster either way, I can change from 900 fps to 1000 fps, which should enable me to fine tune the accuracy.... I can't wait until the snow melts and I can do some long range testing....
Bob
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