Nomercy a double will work fine with slugs, the range will be a lot less though with a smoothbore versus a slug barrel, do as coastie says and check it out, normally the barrels will not shoot the same. Another thing is with a smoothbore double barrel I would keep my shots to under 75 yards and you will have to know where each barrel is hitting at any distance, if I was you I would stick with the pump, one barrel, nothing to confuse you.

The Tazman aka Martin Price
Proud father of a Devil Dog