Gippeto wrote:1/4" brakeline from the auto parts store of your choice. (NAPA)
.177 pellets fit near perfectly, it'll handle several thousand psi, and the best for last....
What I used for my .177 pistol, brake lines tubes make awesome cheap barrels, plus they come with brass fittings you can simply screw into whatever. Also, a 1/4 rigid brake line would be rated to about 10,000 - 11,000 psi burst pressure, no need to sleeve or reinforce for an air gun. Standard bundy brake line is rolled from mild steel sheet, with a wall thickness of of 0.028 inches. If you get bare steel lines (no "poly coating" or galavanization), that works out to an 0.194" nominal inner diameter. When I load my pistol with 0.177 BBs, I use a bit of thin paper or plastic for wadding, but I find that you don't need any wadding for 0.177 lead pellets, they're a perfect seal in a 1/4" tube, and with enough pressure the skirts obturates against the barrel anyways.