Good point! It's overkill but here's an example and the charge holds it form through 3 ballistic heads using glass as the liner.
The only counter argument I can think of is that standard shaped charges need an optimal stand off distance in order to work. If the device was attached to CK's shirt it could've moved too much to be effective and cause superficial injuries and a damaged shirt. On the other hand I think a barrel and projectile would have a larger margin for error. As long as it was pointed in the general direction of the mid neck it would be effective.