Well that is a funny assumption. We actually don't know how heavier slugs from NSAs, KOs, and Zans would perform. I suspect they would do better than the above referenced Altaros. The 28gr slugs did well, and I think a few more grains would not amount to a 6' spread like the Altaros. Regardless, this quick test was with these slugs, out of which the Altaros performed worse than any slug I've ever seen. Does that mean they are all horrible? I should hope not. If you want to see how 30-35gr slugs shoot of a Prophet 1:32 barrel you can always buy one and try it out. If I was a betting man, and sometimes I am, I would guess that
@intenseaty22 could shoot to 39gr~ with pretty good hunting accuracy (not a 6' spread), but that is just a guess.
I will be doing a slug test here pretty soon so I'll grab some similary weighted slugs as the Altaros that I will be testing.