Once you get past the above post of mine, here's what I think.

A Brenneke 28ga slug is a 5/8 ounce, or by my calculation 273gr, moving at 1450fps (Brenneke's number). Hunting with that wouldn't make me weak in the knees. A friend shot a deer with his .54 round ball out of his long rifle and anchored it, and as you point out the two are comparable.