QB79 Ninja - The $200 PCP (PAL Required)

[rsterne]

Here are the results of a full string starting at 3000 psi using the Stage 2 "Maxi-Valve" setup running at a regulator pressure of 1500 psi.... I set the RVA to 2.5 turns out, which set the velocity just where the "knee" of the curve starts, with the 14.3 gr. Crosman CPHPs....



The average velocity was 908 fps (26.2 FPE) with a high of 914 and a low of 902 for an ES of 12 fps (1.3%) over the first 58 shots.... Shot 62 was just outside a 2% ES and wasn't counted, and the pressure at that point was 1300 psi.... As is typical when you tune a regulated gun to the "knee" of the velocity curve, you can shoot a couple of hundred psi below the setpoint before the velocity takes a dive.... The efficiency worked out to 1.07 FPE/CI, which for this power level in a QB79 is pretty astounding....

I'm extremely pleased with the results of this testing.... I think it would be very difficult to get more power than this from a QB79 without major changes to allow running a burst disc higher than the 1.8K which is required for safety the way the gun is produced.... While more power could be produced from a QB78 because of the larger tube, when you consider the simplicity of just screwing a tank onto a QB79 to convert it to a PCP it's a pretty impressive combination.... I will be re-fitting the 1200 psi standard SHP Pro regulator for final testing shortly....

Bob

[rsterne]

I made one more slight change today before the final testing.... The off center RVA screw was canting the cocking block slightly, and I noticed a slight scuff mark on the spring spacer.... I made a longer, one piece cocking block, with an integral spring guide and spring spacer.... The new cocking block is 1.25" long, of which 0.25" is a spring spacer that is 0.34" diameter, the other inch being full diameter to eliminate it canting in the tube.... That allowed me to shorten the RVA screw and just tidy things up a bit.... It shouldn't have changed the performance at all, but in fact I picked up about 10 fps, and gained a bit of efficiency as well.... The Preload numbers have changed, as I can't put quite as much preload on the spring at maximum with the shorter spacer.... Here is a new graph of Velocity and Efficiency vs. Preload using the JSB 15.9 gr. Exact Jumbos pellets....



As per my usual practice, I selected a preload on the knee of the curve, just below the plateau, in this case 4.5 turns out.... I refilled the tank to 3000 psi and shot a string with the following results....



I got 80 shots between 844 and 856 fps, an ES of just 12 fps (1.4%).... and was able to shoot down to 1100 psi before the velocity dropped below 840.... The average was 849 fps (25.5 FPE) at an efficiency of 1.21 FPE/CI.... During shooting the string, I shot 5 shot groups and sighted in the scope in my 20ft. indoor range.... By the time I was done, it was punching group after group in the same place on the target that were only 1/4" across, barely bigger than the pellet.... I can't wait to try this rifle out at longer ranges.... This is just about the perfect velocity to shoot the 15.9 gr. Exact at, putting it right in the middle of it's sweet spot for the Ballistics Coefficient....

This has been an exciting project, and I'm extremely pleased with the final outcome....

Bob