John, according to RIA, this has a fixed slug choke, so whether that is fixed cylinder, improved cylinder, or modified is anyone's guess. It does not take screw in chokes. Have a great day!

John, it does not take screw in chokes and has a fixed slug choke. Most manufacturers use a fixed cylinder bore for slugs for best performance with Foster Type Slugs in smooth bores. Cheers and stay safe!

John, looks like this has a fixed cylinder choke, Wich rock island considers a slug choke. So this does not take screw in chokes. Sorry but hope this helps.