Hi Glenn, it comes with improved cylinder and modified chokes, yes you can shoot slugs, but not through the modifed choke, according to Stoeger. . The owner's manual states "Our firearms are designed, manufactured and proof tested to standard based factory loaded ammunition."
Stoeger - These chokes are recommended for slugs:
4 notches = Improved cylinder
5 notches = Cylinder
A cylinder choke is recommended for shooting rifled slugs in a smooth-bore barrel.
It is not safe to shoot slugs through chokes tighter than those listed here.
.
Do not shoot Sabot slugs through a smooth bore barrel.
Slugs usually have best accuracy with IC choke, do not shoot slugs through a full choke.
Stay safe & have a great day!