Tennis Ball Barrels
Tennis ball barrels are made of 2.5" PVC, which is a standard size, but is extremely difficult to find. Even if you do find the 2.5" pipe, it is almost impossible to find adapters for using it on your chamber. You can probably find them at mcmaster.com. There is no way to describe the feeling of shooting tennis balls. They feel so much more powerful than spuds. One aspect of shooting tennis balls is that they are an extremely predictable projectile. They are also very reliable, cleaner than spuds (think no spud juice!) and are very consistent. Tennis balls work very well in both combustion and pneumatic launchers.
This is a pic of me holding my gun with the tennis ball barrel attached.