QB Project

[happymecanic]

While waiting for my XS60C to be delivered, I'm working on another CO2 rifle project. A beaten up QB78 I'm rebuilding with a QB79 tube, a custom open end valve and a custom made tank block for 88-90 grams CO2 cartridge.

The rear half of the valve had the threaded part shortened to 1/4'' and the O-ring groove has been lightly re-cut. The front half have been shortened to 1 3/16'', and a O-ring groove cut in the front part of the OD. The inlet port have been rounded to help flow.

The tank block is made of 17-4 stainless steel, it has 4 O-ring grooves. It's hanging the cartridge downward, with a rearward angle of 15°. I hope this will help make the gun not too front heavy, also it may help the balance with a lower centre of gravity. There's an adapter between the block and cartridge that allows me to remove the cart even if it's not empty. By slowly unscrewing it, I can also easily de-gas the rifle.

The valve and tank block will be pinned with three 8-32 screws each, for an eventual HPA conversion. Other than that, the rifle will have a Lothar Walter 23'' barrel, a custom cherrywood stock and a good set of sights (or a scope?). I'm still waiting for the main tube and some small parts, but the project is well started .

[Gertrude]

that's pretty cool,
looking forward to seeing it's progress.

[happymecanic]

No parts yet, but I started on the stock. Here you see it with a QB78 tube and trigger group (still very rough!).

[Rob M]

Really nice work @@@
some good news is that the 90 gram tank has been burst tested to 14,000 psi. I too made a similar adapter not long ago
http://www.network54.com/Forum/275684/message/1466284816/pumpmman2289+heres+the+preview+pic%2C+thats+all+i+got+so+far
 a rough version of yours made for using the 90gram on hpa

[happymecanic]

Thanks Rob! Very interesting post! I'm not quite sure about using spent 90 grams CO2 cartridges as HPA tank, but a 13 cu. in. bottle would be a nice fit. However, ''low pressure'' HPA (no more than 1500 psi) could be a viable option. I'll need to get infos on that

[Rob M]

 He at first would not reveal the results, just pics. He feared someone would misuse the info.. When i made my adapter he posted the info..heres the burst test and the man who did it posting in reply( keep in mind 14,000 is more than double the failure on a disco)

http://www.network54.com/Forum/275684/message/1465857260/has+anyone+tested+the+burst+pressure+of+88-90gram+co2+-+found+this+no+details

[happymecanic]

He also mentioned that it was burst pressure, and that deformation occured before; to what level, he doesn't say. However it MAY be safe for 1500 max psi, considering a 3:1 safety factor, which makes it 4500 psi. But I also wonder about the steel itself, if the grade/alloy allows continuous inflate/deflate cycles like a ''real'' HPA tank. Interesting discussion, Rob! 

[Rob M]

y

He also mentioned that it was burst pressure, and that deformation occured before; to what level, he doesn't say. However it MAY be safe for 1500 max psi, considering a 3:1 safety factor, which makes it 4500 psi. But I also wonder about the steel itself, if the grade/alloy allows continuous inflate/deflate cycles like a ''real'' HPA tank. Interesting discussion, Rob! 

yep, just food for thought,/hows the qb coming

[happymecanic]

Still waiting for parts to arrive  (main tube, valve and some other bits and pieces). Did some good progress on the stock, only the fore stock left to shape, and then sanding and finishing. Should be able to make progress this week.

[Geoff]

the stock is looking very nice

[Rob M]

man thats a lot of sawdust ! awesome work

[happymecanic]

Thanks a lot, gents! Also you wouldn't believe the incredibly sweet smell when working on cherrywood!

[2K1TJ]

Beautiful work! Love the lines of that stock. Can't wait to see it finished!