The only problem I’ve ever had with bullet casings or regular steel blunts is they tend to skip and deflect easily. When I was in Ontario in 2006 I did a lot of mid-day grouse hunting. Those birds are basically like trying to shoot a regulation size softball covered with feathers.
Using regular steel blunts, if my shot was dead center the arrow would penetrate both sides of the bird and bowl it over on the spot. Nothing to it. But if my shot was a little off center the arrow would knock the bird one way and glance off in the other direction. Then a foot race would ensue between me and the wounded bird.
By shooting a head that grabs, like a Hex Head or Judo, even if my shot wasn’t dead center the bird would be knocked dead on the spot. If the arrow doesn’t glance off, it delivers all its energy into the animal. They’re much more affective and humane, in my opinion.