I had to deer hunt in Ohio with slugs since a kid. We’ve only had rifle last few years. Anyway became involved in the perfect slug gun, building slug guns, shoots, ect. I ended up using Brenneke myself. For serious shooting we are talking under 1” at 100ft. You couldn’t depend on standard slugs to do that. At one time we would use the hottest slug out, 2.75” mags ect.
Rem, Win or Fed. You can dump out a few boxes of standard slugs. Pick up each one and shake it. If it rattles you have a flyer. Brenneke are not Fosters and aren’t necessary for HD. They also have more penetration than standard slugs. I do think #4 buck much better HD load. I’m not much of a what iffer to worry about over penetration but I don’t like to miss.