QB78/79 parts/seals needed

[bigHUN]

So I finished converting my QB from CO2 to 800 psi air,
it toke me some fingers greasing to route a tube from the front cap, inside stock, down to the rear bottom side of the handle grip.
Now finally the air coil is freely hanging on the back below my elbow, all holding pressure owernight.
The problem I am just struggling is
an offset hole on the cylinder between the brass valve and the archersairgun aluminum breach block.
I replaced a seal again and again nomore in my drawers,
- is there anywhere I can order that 7x2.5 mm seal in thicker let say 3mm thickness?
I don't think another brass valve would solve the problem if the hole is offset in the steel cylinder, I can file them together but still the seal height (I guess) is critically low.
Also, could happen that I am feeding just way too much air through the valve. I saw some solutions with a back screw replacing the hammer spring,
- any other idea for diy?

[Doc Sharptail]

If you have access to a drill press, you can mill a flat over the brass valve t.p. hole with a 1/4" mill cutter bit, and use ice maker tubing.
Stock QB t/p seals won't hold much more than C0-2 pressures.

I found that if I rotate the mill cutter by hand 5 or 6 revolutions before starting the drill press, chatter is greatly reduced.
Mill cutter bits are available at machinist supply stores, and are actually a surprisingly modest investment.

I use a small tubing cutter to cut the ice maker poly tubing. I put the shaft of an appropriate sized drill bit inside the tubing to support it while the cutter wheel is doing it's work. Usually end up with very square cut ended poly tubing. I don't worry about the contact on the breech/barrel side- the tension of tightening the screws is enough to make a proper seal on that end, as long as the poly tubing is cut properly square.

-D.S.

[bigHUN]

Thanks for the tip. Yes I have a micromill and have some endmills as well. Today Im doing homework.
What I figure, the upgrade breach block have a ballnose grove on bottom to "seal" or sit on top of the main cylinder but that grove is not wide enough and with a magnifying glass I can see the port seal. It must be blowing there I can feel on my palm head the kick.
Where can I find that tubing?

[Doc Sharptail]

Where can I find that tubing?

What I use is marketed by Watt's.

"Polyethylene Tubing, 1/4" O.D .x .170" I.D."

Rona, and Home Depot carry another branded version of the same thing- either by the foot, or by pre-packaged lengths...

in the plumbing dept. IIRC, the minimum pre-pack length is 25 ft... pressure rating is 140 psi un-supported for liquids. I've been using it in my un-regulated A/R-20-78 at 3 K psi- and that is under compression between the valve and breech/barrel....

Edit: The above pressures are based on a full length, tested, replacement Derek Vineyard HPA/PCP tube, and do not apply to the far lower pressure rated factory QB/AR tubes....

-D.S.