well if it is a full choke barrel i assume you mean that it is not threaded for choke tubes, and its just a full choke bore? If that is the case then no you wouldn't be able to use any after market choke on it without some serious gunsmithing or a new barrel. But like i said if it is a full choke bore then you shouldn't really need a choke, the constriction that you would get from the choke is built in the barrel. Assuming all that is true i would pick a box of turkey loads and see how it shoots from 20 yards, then 25, then 30 etc. That way you can find your maximum range and see if any holes in your pattern develop, if so try different ammo. practice a couple close shots too because that pattern is tight right out of the barrel and its easy to miss if you aren't careful and don't know exactly where your gun shoots. The extra constriction that you get from a super full/turkey choke means the pattern is tighter which helps extend your range a little bit, but out to 30-35 yards that turkey will never know the difference