OK, maybe I will defer to your advanced knowledge of muzzleloaders, just this once. I may be talking about a patch puller. Do you know what I'm talking about? It has two curved little metal pieces on the end - just like in the original post description - and is apparently used to pull a lost patch from the bore (rather than a bullet). Picture one of those prongs getting caught in a bullet and breaking off when the soldier yanks it out. Is that plausible? Certainly it makes more sense than someone going to all the trouble of embedding a piece of curved steel into a minie ball, totally destroying any kind of decent flight characteristics and any possibility of hitting what you're aiming at, all in the hopes of inflicting more injury than you're already going to cause with a chunk of lead the size of your thumb.
Oh, and don't ask me why the guy is using a patchpuller in a loaded gun. Maybe he's stupid, maybe he lost his bullet puller, or maybe, like me, he thought that's what the tool was for. I don't know. I'm not in the habit of defending Yankees, but I'm just looking for something more logical than a "diabolical" plot.