Copper pipe and fittings are rising in popularity as a spudgun construction material, particularly amongst UK based spudders, due to the rarity of pressure rated PVC in the country.
The primary advantages of copper pipe are that it is rated to much higher pressures than PVC, and has better failure characteristics due to it's high malleability preventing shattering. This makes it well suited for making high pressure pneumatic cannons and hybrids. It is also typically internally very smooth and consistent, which combined with it's high rigidity makes it exceptional barrel material. Copper pressure ratings have a safety factor of about 7.
It is more expensive than PVC (especially larger dimensions) and considerably heavier, and is therefore mostly used for small caliber cannons (1" or less).
Types & Use
Copper pipe is usually joined by sweating, using compression fittings, or Copper epoxy. The latter two are slightly more expensive, but require minimal tools to use. Threaded fittings for copper pipe are usually made of brass.
Copper pipe comes in two tempers, annealed and drawn. Annealed copper pipe is very soft, and can usually be bent by hand. Drawn copper pipe is rigid, and will flex rather than bend (to a certain limit). Drawn pipe is the most useful in spudgun construction, since it will keep its shape and not get damaged easily. It is also rated to about twice the pressure as an annealed pipe of the same size.
Copper or Brass pipe/fittings should not be used with acetylene gas, as copper alloys can act as a catalyst to the explosive decomposition of the gas.
Due to it's relatively thin walled nature, potentially dangerous "sharp" ends can exist on pipe ends that have not been cleaned, and anybody using it should be aware of this.
Cutting of copper has a high attrition rate on rotary multi-tool abrasive discs, which will wear down at a high rate, and break apart regularly. Use of safety goggles is doubly recommended