I've experimented a bit with soft metal broadheads and a simple copper point type made by wrapping a cone around the tip of the shaft, tacking it in place and filing the tip. Some of the brass became quite work-hardened from having to hammer them back into shape after just about every shot. The copper points were OK fired into a bale of hay, but didn't last too long even then. This was many years ago and I was only messing with it I had a bunch of sheet metal left over from a metalworking and jewelry class, no experience at the time working with even mild steel, and no money to just buy target points.
Anyhow, just from my brief hands-on experience with copper and brass points, against any type of armor they would be useless, but use against unarmored or leather-clad opponents would probably be classified as a war-crime if practiced today. The hollow-point bullet analogy is accurate, but on a much larger physical scale: My soft metal points almost always curled in one direction or another if they hit any firm resistance, turning into a hook shape. I made a shredded mess out of those haybales, and I got pretty sick of digging them out. I don't want to dwell on what if would be like to be shot with something like that with no armor, especially when the first thing you'd probably do is try to pull it out. Ghastly.
That being said, I still plan one day to make some silver points out of some coins, hamming them to shape while trying to keep some of the original engraving. Of course I'd never actually shoot them, I hope, but it would be cool just to have them. And comforting in my case, I'll admit. I don't believe in werewolves, but that doesn't keep me from being afraid of them.