i also found the answer....seems like BRENNEKE designed the rifled slug to be able to shoot through any choke. the ribs on a rifled slug provide space for the slug to compress as it passes through.
Yep, everyone did it "forever", untill the internet came along and someone said you couldn't.
I shot some Rem. foster style slugs in my 1935 side by side (full choke bbl) a few days ago, and they shot pretty good. I've been shooting them in it for 25 years, and there's nothing wrong with it's bbls...
Do you supose a modern bbl made for STEEL SHOT would be even thicker and evenstronger???
DM