Look up the "QB79 Ninja $200 PCP" thread, you should find everything you need there.... The regulator output threads into the tank block the same as a CO2 tank.... The fill fitting and gauge interfere with the barrel so you cannot unthread the tank without removing it, so I would forget about removing the tank when full....Bob
Regarding the modifications for power, Bob's $200 PCP thread is indeed the foundation you need. Modifying the bolt is just a matter of enlarging the hole in the nose and then enlarging the hole in the side. Pictures are in Bob's thread I'm sure and I also have pictures in the thread linked in my signature. Stepping up one numbered drill bit at a time as Bob describes is a good way to keep it centered and avoid blowing out the side wall. For the valve, I felt like fabricating the spring guide was a bit over my skill and equipment level. I think using a conical spring as described in my thread is about as drop-dead simple and effective as you can get...assuming you can source the spring. Otherwise the mini-valve, as it has been termed, with the return spring moved to the opposite side is another approach that is relatively easy to pull off with somewhat primitive tools. All you need is a 3/32" E-clip and a spring from an ink pen. To cut the groove for the E-clip, spin the valve stem with a drill (drill press is preferred) and use a thin emery wheel in a Dremel to make a shallow groove.
Yes, you can make a mini valve from the stock QB valve rather easily. Lacking a Dremel, I suppose you could use a small rat tail file or diamond file to cut the shallow groove. Or keep your eyes open for a Harbor Freight rotary tool on sale. They have a single speed for as little as $10 but you really need to be able to slow it down for many types of work. A variable speed is only $25 on their site right now. For the spring, the dimensions and spring rate aren't critical. You just need a little something to keep the poppet against the valve seat when the tube is not pressurized. Otherwise when you pierce a new cartridge, you'll lose some CO2 before the pressure builds enough to slam the poppet onto its seat to seal off the system. It just needs to be small enough in diameter that the E-clip will hold it in place, and short enough that the valve stem can move at least 1/8" before reaching coil bind (the point at which the spring is fully compressed). If it's too long, you can trim its length. If so, be sure to put the cut end against the valve body. If instead you turn it the other way, it may thread itself through the gap in the E-clip.
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