It’s not felony murder. That’s when someone is killed during the course of a felony and all involved are held equally culpable. Like the get away driver for a bank robbery when someone is shot. He’s got the same criminal liability as the one who made the shot.
Right, that's exactly my point: they were committing a crime already, and that crime resulted in someone's death. So maybe even if grabbing at someone's shotgun would normally prevent you from being charged with murder, they would still get felony murder because they feloniously assaulted the man.
I'm not a lawyer, obviously.