After a busy Summer in the Motel, I finally got a chance to get back into the shop.... I dragged out the Disco Double, which had been leaking, and pulled the valve because I knew all the other O-rings weren't leaking.... While it was out, I drilled out the throat from 0.250" to 0.266" to make it about 10% larger than the rest of the ports.... While that doesn't tend to increase the power, it does tend to increase the efficiency, and that small change I could do without disturbing the OD of the seat, so that the valve wouldn't be any harder to open at 3000 psi.... I put new O-rings on the valve, reassembled the gun, and that indeed was the source of the leak.... I tested all the barrels, and there was basically no increase in velocity, but the efficiency went up 5-10%, so the experiment was not only worth it, but confirmed my previous experiments with slightly oversized throats.... The exhaust, transfer, and barrel ports are 0.219", and the equivalent throat area (ID minus stem) is 0.241", which is 10% oversize in diameter, and about 20% in area....

During the testing of each caliber I used one pellet and one bullet.... In .250 cal I used the 25 gr. JSB King and my 51 gr. Bob's Boattail.... For the .300 cal I used the Daystate 50 gr. pellet and my 70 gr. BBT.... In the .357 cal I used the JSB 78 gr. pellet and my 127 gr. Boattail.... I tried different preload setting with each until I found the one that would give me a starting velocity just within 4% of the peak for that pellet/bullet.... When I was finished, I decided to put my "Best Tune" picks all on one graph, so that we could see how the different calibers compare, and here it is....



The dashed lines are pellets, and the solid lines are bullets.... black for .25 cal, blue for .30, and red for .35.... All strings except the .25 cal with the JSB Kings (and the .357 with bullets) were shot with the barrel port wide open, and the hammer spring preload adjusted so that the first shot at 3000 psi was just within a 4% ES of the peak for that string.... Therefore, they represent the most powerful and longest string I can get with a 4% ES starting at 3000 psi.... Had I done that for the .25 cal Kings, the velocities would have been approaching 1100 fps (the gun can drive a King at over 1200 fps, WFO), so I cranked in the adjuster that prevents the flat nosed (probeless) bolt from being withdrawn clear of the transfer port a full 5 turns (7 is fully closed).... That dropped the velocity into the 950-1000 fps range, and I know that the Kings are still accurate there, so it seemed like a good choice.... and easy to change my mind on the velocity by small adjustments on the bolt restrictor.... I ended up with 26 shots (over 3 magazines) at over 55 FPE average from the 250 cc reservoir, which is over 1.20 FPE/CI, stellar efficiency at that power, IMO.... The other exception is the 127 gr. bullet in .357 cal. where I got 3 shots within a 3% ES, without regard to the efficiency, which turned out to be 0.62 FPE/CI.... not bad for 170 FPE....

The other 4 strings all ran from 0.91 to 1.06 FPE/CI.... I should mention that if I want to tune those 13-14 shot strings for a single magazine with the minimum possible ES, by increasing the preload about 1 turn I can get less than a 2% ES for 1 mag. at significantly more FPE.... This is always an option to trade shot count for more power and a tighter ES if necessary.... Of course if you want to tune for slightly less power by turning in the bolt restrictor slightly, then those 13-14 shot strings can easily be stretched to two full magazines as well.... Anyway, all in all, I'm very pleased with the final results.... The gun turned out to be good with pellets and bullets in all three calibers.... It spans the range in power from Ground Squirrels to Deer and Hogs, and everything in between, depending on choice of caliber and ammo.... Pretty good for what started life as a Disco....

Bob