RE: What choke for Brenneke KO slug
Try it with the IC and Modified to see which works best. Normally the IC will work best, but sometimes a gun or slug will like the MOD tube. My mossberg and A-5 both shoot a bit better with the MOD tube.
Most rifled slugs can be fired from a full choke, but I don't suggest it. I can't see where it would be good for it, and I doubt it will be all that accurate. The slug will be pretty deformed when it leaves the barrel.
The rifling on the bullets is actually there to crush as the slug goes thru your choke. It imparts no spin what so ever on the projectile. If you want a little better accuracy you might look into getting a rifled choke for your gun.
Paul