'Barrel length matters. It is what lets a paintball accelerate from standstill to 300 fps. At least, the first 7-10 inches of a barrel do that.' from paintballstore.tv barrel guide I googled up.
Well thats where I got my info from, so sorry if its wrong.
trust in the jedi powers of TK, he is after all pretty much the god of stuff like that, I think automags.org has all techy articles like this on, makes for some good reading if your into stuff like that.but i think this is now a totally different thread all together...
Back to the job at hand, as bolter says if your using only the one barrel get a larger bore (.692, .693 depends on barrel manufacturer) that way you can shoot any paint you feel like without worring (sp) about smashing the paint in a tiny barrel i think the stock ION barrel is a .689 which is pretty much an industry standard size as a mid range, most paint will be fine through it but there are a few types that are on the large size, i remember tomohawk competition(i think, definately tomohawk, blue boxed stuff anyway) was .695