Unless there's a * by the title, it hasn't been built yet.

CO2 Cartridge Rifle
CO2 Closeup
CO2 Rifle, with clip
Self Propelled Shell Pistol
Self Propelled Shell #1
Self Propelled Shell #2
*Potatoe Cannon
*Potatoe Cannon with FS for size comparison
*Potatoe Cannon with Bipod
*Tennis Ball Grenade
*TB-Grenade Open
*TBG Backview
*TBG Frontview