Once upon a time, as a young air wing jarhead, I was part of a merry band of young jarheads with more ingenuity on hand than there was official work to be ingenious at. So we came up with the blowgun from Heck. It fire parachute rigger's needles (those things are BIG) using compressed nitrogen from a NAN-2 cart as the propellant. The weapon had a trigger group (actually a valve release) made out of brass in the jet engine shop. We used cut-up IBM punch cards as a combination fin and sabot. A Tasco rifle scope from the Marine Corps Exchange finished off the weapon.
We were bagging rats at 100 meters with our toy...