Haha, that's weird I just finished watching season 4 of Dexter two minutes ago...
From what I understand, ammo manufacturers load their ammo with powder that isn't available to reloaders. So the amount of powder in those cartridges wouldn't really tell you much. My only advice is either to go on feel alone by working up your own load, or better yet to chrony some of those Winchester loads and use that info to guide your load development.