Based on the Gyrojet pistol, a gimmicky weapon developed in the 1960's that fired tiny rockets instead of bullets. The gun saw some action in both Vietnam and a James Bond movie.

Works fine for either Engineer or Scout (or both).

Would fit great for Soldier (the weapon being a rocket gun and all, and would preferably work like differently from pistols, but it's not up to me), but he does not have all the proper animations.
Righteous Bison animations work well enough in the third person, but not so much in the first person.