If there is no choke in it then you probably cant screw tubes in. I would suggest either looking into getting another barrel that you can put chokes it (you would want one with a ventilated rib) or you can probably save some money by taking your barrel to a gunsmith somewhere and have it drilled and tapped for chokes. It is most likely too late to hunt this spring but I dont know the season date for where you live, so you have a while to get the money and get it done. You shouldn't pay much more than $100 or so for the barrel. I might be able to help you find a barrel if you need. Feel free to email me or PM me if you have any questions or want some more help.