I have reloaded for the 300 mag a little bit. As far as going beyond the reloading manuals, unless you benchrest shoot, you are going to find that the manuals are often right on determining the most accurate powder. If its not the most accurate one, then it is a difference of a fraction of a fraction of an inch. If you have a custom rifle with some odd specs here and there, then going beyond the manual can really help. If I were you, I would stick with the reloading manual. With that rifle, I would think that .75inch groups at a 100 yards would be the norm with nosler ballistic tips or sierra match bullets. It will depend on your shooting and the quality of the production at the time they made your rifle.