QB79 Ninja - The $200 PCP (PAL Required)

[bitterman]

Very nice!!!!

Bruce

[rsterne]

Well, sometimes you pay for not keeping good notes.... I made an offset RVA, removed the rear cocking pin to convert to "cock on open", and machined a new downwards slot to hold the bolt back while loading the pellet....



The only problem was, that the version I previously did that on (in the photo above) had a shortened hammer and guide pin on the cocking block to allow the bolt to be drawn back further without the hammer hitting the cocking block when drawn back to the rear notch.... When I adjusted the RVA so that I could push the bolt down into the rear slot, the hammer spring didn't have near enough preload on it.... Rather than modify the hammer and guide pin, I made a spacer to slide over the guide pin on the cocking block to increase the hammer spring tension.... The spacer was 0.35" OD, 0.22" ID, and 0.30" long, so it adds that much preload, and allows the gun to function properly.... I then proceeded to test the velocity at various preloads, with the following results....



You can see the typical plateau in velocity you get on a regulated gun when the hammer strike is more than required.... The velocity doesn't increase, the gun just uses more air.... One slightly unusual thing on this graph, is that the efficiency falls off on the right side as well.... For some reason, the power drops off quicker than the air usage when the gun is detuned below 800 fps in this Stage 2 configuration.... My choice with this setup, at 1500 psi, would be to tune the gun for just over 900 fps (26 FPE).... I would expect about 50-60 shots at that power level.... Pushing for more power than that with a QB79, even with the "Maxi-Valve" simply wastes air....

Bob

[rsterne]

I finished and installed the stock today....



It's a Richard's Microfit Wildcat Thumbhome in Select Grade Black Walnut with Ebony Grip Cap.... beautiful figuring in the grain....



I had to shorten the forearm and inlet it for the tank block and regulator.... The finish is 7 coats of Watco Danish Oil, each coat wet sanded, ending with a white Scothbrite pad of 1200 grit equivalent and then a coat of Dark Minwax.... The scope is a Leapers 3-9 x 32 AO with Sunshade.... The gun weighs 8 lb. 7 oz. as shown.... The Air Stripper is from a Hatsan PCP, I threaded the barrel 1/2"-20 NF to accept it....

It's no longer a $200 PCP, however....

Bob