Davidmil, I have used that style of slug for years. I was drawn to it because I found it much more accurate than foster types and because it was a heavy solid slug that would have damn good penetration. I think the plastic part stays on to act like a fin and help stabalize it. I have never had the pleasure of taking a deer with a shotgun (not yet) but I have done some impromptu tests on wood, wet phonebooks, etc comparing that slug with a foster and found the "rotweille" slug to be much better.

David