Well, I use a homebrew 50 caliber, and while I'm nto an expert, I go with plain paper and bamboo or wire darts.

I take the bamboo (or wire) about 8inches long (the wire) or 15 for the bamboo, wrap one end of it with a small bit of scotch tape, make the cone, tape it into place, then cut to fit the blowpipe....

part of it might not be lungpower, but it'd be breath release, what you want is a full lung inhale, then hold your tongue judt behind your teeth, like your'e tonguing, then since youre' a tuba player, you'll recognize this. BLATTT that breath out like youre' trying to make the band director jump out of his skin.

it should flex your chest in roughly the same manner as a hard sneeze

another thing, and Iv'e almost blown my own self up doing this...make sure the dart slides freely, but not TOO freely. if it's too loose, then all the lungpower in the world won't move it, because youv'e too much air leakage...too snugly, and it'll weld itself to the inside of the pipe with pressure, and youre' fighting friction. A good fit would be where your dart will only just slide down the tube if you dip the business end of it.

http://slinging.org/forum/YaBB.pl?num=1184730650/11#11 Info on Darts and Pipes  

if you're having trouble getting your cones to work, get a small piece of cork, stick it to dart, and shave it to barrel size, i havent yet tried this, but heard it works very well.
BTW, I'm a drummer if ya couldn't tell by the name. hehe, Bass drum 5, biggest marching instrument on the field

I just pulled out my blowgun this weekend. It's PVC, and the darts are duct tape and coat hanger wire. My cousin, who was visiting, made his from copper pipe - expensive, but much better.
Needless to say, that's on my list.

As for distance... We lost a few in a snowbank about 50 feet away.