anyone know where to find pipe suitable for barrels? preferably specific to the calibre of ball for all balls (this is all biggun)
Steel brake line (available from many auto parts stores) makes good barrels. They're not tight tolerance, but the material is easy to work with and practically jam-proof. For 1/4" balls, you use the 3/8" OD material. For 7/32" balls, you use the 5/16" OD material. For bb caliber, you use the 1/4" OD material. I do not know of any brake line size that is suitable for 3/16" caliber shot.
I know that the hobby store near my house sells all manner of metal tubing (brass, copper, aluminum, etc) in many different diameters and they come about 3' long. That might be an option for you...
If you find the thick wall, 1/4" brass tube at smallparts, it will just barely nicely feed 3/16 bearings. It is .028or .029 (I don't recall right now) wall thickness. Mcmaster's stock, when I have bought it has always come in at .032 or thicker wall, and will not feed 3/16. -Greg