Yes you can fire foster style slugs in full & ex-full chokes with no harm. The foster slug is made with a hollow base and fins on the side to allow them to swage down when fired thru choked bbls.
I've heard a lot of claims over the years about the hollow bases, and the fins on the sides. So let us flush a couple of these old wives tales. The hollow base doesn't expand to fill the bore. To do that it would have to sit directly on top of the powder charge, It doesn't. The fins on the sides of the slugs don't make them spin. The are there to allow space for the slug to swage down when passing thru a choked barrel. What keeps them flying straight is the shape similar to the shuttlecock of a badmitten game. Majority of the wt forward with a lighter trailing skirt to keep it nose forward.
