Just get a rifle barrel that will shoot 3 inch shells. I don't even know if mossberg makes a 3.5 inch slug barrel, and if they do you are going to have trouble finding slugs for it. And if you do find them, I wouldn't want to pull the trigger on it. The barrel obviously has screw in chokes, mossberg doesn't make a pump gun without screw in chokes. NEVER shoot that gun without a choke installed. I'm really surprised it didn't come with three chokes? The 500's come with an IC, Modified and full choke, I figured the 535's would come with more than one as well.

Paul