Umm, probably not. Might depend on the manufacturer some are slightly different diameters but most will probably not just drop down a barrel, and they certainly won't drop through a modified choke.

A modified choke will work for slugs, some of my guns have actually done better with a modified choke. The norm is the more open the choke the better though. A foster type slug will not hurt your gun or choke so don't worry about that. You will just have to clean it really good when you are done. A foster or rifled slug (same thing basically) will conform to your choke as it passes through. This is what the fins on the slug are for, they crush as they go through the constriction of the choke. They don't actually impart any spin at all to the slug. You can shoot them from a full choke if you want, but normally they are not very accurate because of how badly the tight choke deforms the slug.

The only way you will know how it shoots is to put some in there and see what happens. You will not hurt the gun though so don't worry about that. You will just have to scrub it a bit harder when you clean it is all. It will probably leave some lead build up in the choke.

And try as many different brands as you can, some may shoot considerably better out of your gun. DO NOT USE SABOT SLUGS, they are made for full bore rifle barrels. They will not shoot worth a darn, will be expensive and may possibly damage your choke since they are not designed to crush like a rifled slug is.

Paul