Shotgun shine
This is an expression related to the blueing of a gun - specifically a high-end shotgun. In the South especially, a finer shotgun would have a "blueing" or a "blue" of the steel that was accomplished by way of the quality of the steel and the effort of the person who owned the gun polishing it. "Shotgun shine" is a simplification/symbolism of this concept and a way of saying that a person has a killer instinct; however attractive they may be. It's not necessarily a positive expression, and surprising that in the nearly 25 years since Alabama 3 used it, and since the Sopranos used it in this manner exactly, that no one else has put it on Urban Dictionary.
It's a shame about little Johnny Sack - he's got such potential in real estate, but also that shotgun shine.
shotgun shine
Comes from the"shine" definition "to do big things". To do big things with a shotgun.
El Mariachi really had a shotgun shine when he killed everyone in the bar.