SpudFiles

Has anyone used carbon fibre tube for a 9mm barrel or similar size?
Claims to be: "lighter than aluminium- stronger than steel)

PS,... I live in australia where nanny's rules apply, so no rifled
barrels without a license here unfortunatley.

Assuming that this is the tube which is wound at the correct angle for pressure vessel use, it could certainly be done - the tensile strength is there, and the tube won't be significantly permeable to room temperature air if it's designed as a pressure vessel. The Young's modulus is somewhat lower than steel so the barrel would expand more than its steel counterpart on firing, but this is unlikely to be of concern to you.

I'm curious as to how you plan to attach the barrel onto the gun though - epoxy it into a tube with a threaded end and an internal diameter to fit the external diameter of the barrel?

Carbon fiber is usually better suited to large, mid-range pressure designs (E.g, kilo-psi level) where mobility is important. Steel probably has more favorable characteristics in the sizes you're suggesting, being cheap and readily available in a large number of standard dimensions.
And if you can't find it, just buy a 9mm reamer and the closest undersized tubing available.

Also, the matrix(poly resin in this case) will be the limiting factor. Barrels tend to take a lot of abrasive wear in normal use, so you'll be shaving resin away with any type of hard projectiles.

@DYI...I am going to use - (12mm carbon fibre tube) for my outer barrel now.....
Going to put an air-soft 650mm x 6.03mm "inner diameter" barrel tube inside
the 12mm (outside diameter and 9mm inside diameter), carbon fibre tube for
more accuracy and less wear...

To seal/join it to a 1/2 inch Alpha qev valve....screw in a 1/2 inch (npt) male joining
nipple out of the firing (breech/barrel) end of the qev valve...
Slide a 1/2 inch brass tee nut over the the 12mm carbon fibre tube
and tighten it to the 1/2 inch male joining nipple. (Just the same as if you were joining
1/2 inch copper pipe)..... Put a small magnet at the breech
end of the inner barrel first, to stop the 6mm bearing/plastic bb from dropping in qev
valve, and also running back-down the barrel (if using steel shot).. I just use it as
a muzzleloader until i make a magazine to suit.

I used Carbon fiber as a barrel once, it worked for a while then split, the splinters arent health aswell.