what size?

[spud man]

What size barrel would be better for a peunmatic spud gun with a 4" chamber 2"or 2.5". What size barrle dose pop can's fit in.

[noname]

They fit in 3" I think. You can get some small cans in 2.5," like Red Bull.

[Velocity]

2.5" SDR-21 is very rare, but is the perfect fit for soda cans (IIRC)

[boilingleadbath]

Normal soda cans are 2.6", within a couple thousandths.

Satisfactory barrels can be made from sleaving 3" sch 40 inside 3" sch 40, which I calculate would give an inside diameter of 2.61".
Alternativly, you can find some 2.5" SDR 26; inside diameter is 2.635"