I have recently finished a coaxial pneumatic. The OD of the barrel is .75", and the ID of the chamber is 1.255". While this cannon works, it seals very unreliably, for the barrel support which I built was a strip of copper bent in an attempt to center the barrel. This support does not work very well, and the piston is almost always sealing the barrel at an odd angle.
I need some suggestions on a barrel support which will not decrease flow, and will center the barrel. The easiest solution would be to just pound a nail 1.25" long through the barrel and that would support it; however, due to my configuration, I cannot do such a thing. I would need to pound a nail through the entire coaxial chamber and through the barrel; this would be difficult, and probably lead to leaks.
My idea would be to take 1.25" PVC rod, and cut a .75 hole in the center. On the remaining material, I would drill as many holes as possible, to allow the air to flow through the support and out the barrel. Would this decrease flow a lot?