You might try Gunparts Inc. for a mag.
Use the same positions you would use in the field. Offhand,propped on a post or tree trunk,kneeling. Quality practice is what is important,not quantity. Make every shot count. Remember to squeeze the trigger. Don't jerk.
I have a 30-06 that shoots to same point of aim with M-2 ball ammo as Rem. 150 cor-locs. So I use the M-2 for practice. It is better to shoot what you hunt with so as to be comfortable with your hunting rifle. Kinda like an old friend.