Well my dad is actually gonna hunt this year so he is gonna use his gun come regular season and I am gonna use my break open 20 gauge what size of shell should I use in this?I aint shot it in a few years cause I've been usen dads gun just wonderen what size has the best patteren/distance...and the gun has no choke screws so just gonna use regular ol' no choke.

Since your gun doesn't have choke tubes what is it choked?
Not a lot of info to go on, but you might try the 3" Federal Flitecontrols. The Flitecontrol wad might extend your pattern a bit farther since I doubt your barrel is choked tighter than "full".
If you decided to go with the Heavyweights, the #7's (if you can find them) work very well.