I recently shipped my 590 barrel to KKF to get it threaded for chokes. I've got a nice steel MOD choke for goose hunting. Now, i figured i may use this for slugs. However, i've gotten conflicting reports. Mossberg says to use IC for slugs. TRUCHOKE say to use the least constrictive possible. Wouldn't that be a CYL ?

I did some searching on the internet, and gotten about a 50/50 IC and CYL. If it matters, i'd be using rifled slugs, 12GA. Brenneke.

Improved Cylinder is the most restrictive choke you can use safely.  It may also give you the best group with non sabot slugs.  If you're using sabot slugs, try to use a rifled choke tube.

Cylinder will work just fine, but may not be as accurate.

IC is my choice because you can switch from buckshot to slugs with no problem and it's the most commonly recommended choke for defensive shotguns.

Quoted: Improved Cylinder is the most restrictive choke you can use safely.  It may also give you the best group with non sabot slugs.  If you're using sabot slugs, try to use a rifled choke tube. Cylinder will work just fine, but may not be as accurate. IC is my choice because you can switch from buckshot to slugs with no problem and it's the most commonly recommended choke for defensive shotguns.

Improved Cylinder with a rifled slug in a smooth bore.

does that go for all shotguns???

The short answer is yes but you can try different chokes and see how they work for yourself. MIKE.