Off the top of my head, Angel Heart (1987)
has a girl (Lisa Bonet
) killed in that manner, but I don't remember if they actually showed the act.
They definitely didn't show it, it was only mentioned in dialogue.
This rings a bell... I'll keep thinking.
GATOR BAIT is a good bet... I think a shotgun was used. Do you remember it it was a shotgun or handgun?