The Benneke's had the VERY deep grooves to easily compress in chokes. The American Foster slugs and the shallower "rifling' grooves and hollow base to compress when used in choked guns.
The Fosters were also smaller than the bores of most 12 gauges. The Remingtons were the smallest, at .690", with Federal and Winchester closer to .710" to .724". Now, I haven't measured these myself. I'm just going by memory on the article I read a long time ago.
I would say, if you have a mould casting a solid slug that is bore size to your shotgun, do not use that in a choked gun.
Factory slugs, Brenneke or Fosters should be A-OK.

edited: the forum is working nicely.