I tried to glue up the 0.047" vent through the poppet and redrill it with no success, so today I made a new poppet for my SS Valve.... I am still using the 3/8" big end and 1/4" small end, but I added a thin (1 mm) O-ring inside against the shoulder of the poppet as a bump stop.... It should never touch, but if the valve was driven fully open (or blew fully open) the O-ring bumper would take the shock instead of either the shoulder on the poppet hitting the inside shoulder of the thimble, or the spring going coil-bound.... It was just a safety measure, but also a way to find out if the valve was opening that far.... As I expected, the O-ring made NO difference, which is proof that the valve is not trying to open more than the 0.19" travel before the O-ring hits.... This was a useful piece of information (and expected), and I plan on incorporating this feature into any future SS valves I make to insure they don't break from being overdriven, or from machine-gunning.... I used PEEK for the poppet, not because it was required, but just because I had some and wanted to try it, and it machines nicer than Delrin....
When I reassembled the 6 mm regulated gun I finally nailed it.... I used the 32 gr. MDS hammer, and the 11 lb/in spring with 1 lb. of preload on the SSG guide.... I was able to easily get to the plateau with all three bullets, and have to run 5 turns of SSG gap with the heaviest and 7 turns with the lightest to get about 3% below the plateau, where I want to operate to get reasonable efficiency.... Here is a graph of the velocity vs. SSG gap for all three bullets at 2800 psi....
I am getting nearly 200 fps of adjustment before the valve falls off the cliff, which is plenty, I will never run it that low.... You will note that there is one additional line on the graph, the dotted black line.... I set the SSG gap at 6 turns, and using the 63.8 gr. bullets I tested the velocity adjuster on the back of the receiver that restricts how far the bolt retracts by moving a pin into the J-slot for the handle.... The reason for the slight increase in velocity when the adjuster is turned in 2 turns is that I had to shorten the nose of the bolt 1/16" because it was pushing the bullets too far forward, which made the 73.4 gr too hard to chamber.... This meant that with the bolt handle pulled all the way back in the J-slot it was creating more wasted volume in the chamber, behind the barrel port, which was dropping the velocity slightly.... It shows the importance of minimum wasted volume between the valve seat and the base of the bullet.... From the maximum velocity setting I have 8 turns of adjustment on the 8-32 screw, which moves the bolt nose from the back of the port to nearly obstructing it.... at which setting the velocity is below 500 fps.... The cool thing about this adjuster is that you can easily try different velocities, to find out if there is an optimum for accuracy.... Of course you should adjust the Harmonic Tuner at each velocity, just to make sure what you are seeing is a true velocity effect, not a change of accuracy due to barrel harmonics....
Once I am sure that there are no leaks, I will remove the "tiny tank" and replace it with my 500 cc CF bottle.... At that point I will be able to test the efficiency at various velocity settings.... These two guns are nearing the end of their development, which is a relief because it won't be long before the Motel gets busy and my shop time disappears once more....
Bob
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