For those bitching about the penetration, that damn projectile looks as heavy as an entire .45-70 cartidge!.If he had a much smaller bullet the velocity would be sonic and make for a nice cat killer.
Creativity: C +it's been done before.
Execution: A - Miles better than the mile of wire crap, or BB guns out there.
Practicality: B- If this thing were to use a much lighter and smaller projectile the efficiency would be better too.
Obamanomics: F- Beats using a slingshot on ferel cats on the cool factor but slingshot ammo is dirt cheap.
Wouldn't the penatration get worse on a lighter cartridge? Needs to be much thinner like most hand fired Flechette rounds (only a few mm).