I haven't called EMI to ask but based on what I've read they have not been very forthcoming on density numbers. Tuleman, They are magnetic, I picked them up to count them with a magnet. Based on anecdotal observations the #4's seem to perform at least as well as steel 3's. That's from my own shooting and watching a friend shoot them. Pattern wise they were in the 63% range with an IM for me at 40 yrs out of an 870. I really want them to be an improvement over steel but I'm still skeptical. I think I'll buy another box to pattern in the off-season.