You sure got right on top of that little bunny, he is in trouble.
I was making blow guns when I was in the 25th ID at Schofield Barracks back in the late 70's.
I did a pretty detailed study of how much air a man could push in one breath by blowing up ballons and measuring them. I finally figured out that a .375 inch tube six feet long was just about the ideal for me (at the time a 28 year old runner). Anyway I settled on using golf tee's as the flights for my darts and bicycle spokes 6 inches long as the points. I pounded down the ends of the spokes flat and shaped a double edged broad head on them, much like the darts you are shooting.
At twenty feet I could shoot one of them through a mature banana tree. For those that don't know a banana tree is about as soft as an onion and 8 to ten inches thick.
As it turns out, you can get .375" tube aluminum tube and plastic golf tees and bicycle spokes at about any hardware store. The tube comes in 8' lengths so you can get two 4 footers out of one piece. For hunting though you'll probably want a five or six foot tube.
There is a lot of information on the web about blow guns now days.
