New 870 Barrel

[Maxamillion_16]

Hey guys, i just bought a used 20 gauge 870 express Magnum it shoots 2 34" shells and 3" shells. I t came only with a Hastings paradox rifled slug barrel. I am going to buy a vented rib barrel for it, but does any body know if the magnum makes a difference for the 20 gauge or can i just get a standard 20 gauge 2 34" and 3" 870 barrel?

Thanks ,
Max