My vote goes to the one-piece Dye Boomstick (no one's mentioned it yet?). I always have a supply of these puppies for different markers, and it's the one barrel I can count on working ALL the time. The older, glued one-piece ones are the only ones I've owned, and they've never let me down. I have had extremely good success with it on an Autococker, Intimidator, Viking, Impulse, Phantom, and my Bob Long Millennium (Spyder clone). All worked with extremely accuracy and they look great too! Don't go for the knock-off boomsticks (3A paintball, JT, etc.), get the real deal used on PBNation, should be able to find one for $30-40, much cheaper than their $110 retail! 14" is a good length, although most of the ones I buy tend to be 14"-18." Length doesn't matter much past 10", it just looks really intimidating!
** Spin Doctor's Paintball Page
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** PBN Feedback (old) Agglet re: Frink: "Much like a newborn baby your collection is both beautiful and disgusting." russc: "PBN is a business, and that's why they prefer thousands of morons to hundreds of intelligent posters" drum: "Between the ammo shipments and all the long rectangular packages, not to mention regular mail from the Pa. Superior Court, my mailman is pretty sure that I am a freak."