If you're planning on shooting the 300 to about 500 yds or so, the really heavy, high b.c. bullets aren't going to add that much to your shooting other than recoil. Things don't really get interesting until you pass the 600 yd mark. Then things start to get funny. You might want to look at the 190g SMK though. I've never shot any, but my gunsmith shoots them out of his .30gibbs at Williamsport in 1000yd benchrest comps. That might be the best combination of b.c. and weight for that case. My other choice would be the 178 AMAX. Like I said, don't worry too much about the b.c. for under 500 yds. Just shoot the one that you barrel likes the best. It's all about bullet placement, not bullet type.
FYI, my experience with the barnes bullets out of 2 different guns was that it took a lot of fidgeting to get them to shoot. I never did get them to shoot good enough for what I would call a long range bullet.
I don't think your going wrong with the premier reticle. Again, I've never used one, but everyone that has one absolutely loves it. The 6 to 18 will work plenty well to 500yds. I shoot a fixed 20x on my long range gun and have had no problems. The benefit you will have will be target aquisition on lower power then you can "zoom" in to 18 for the shot.
One other thought. You might want a brake on your gun if you want to see bullet impact. The recoil of the 300 will definately not allow you to see your hits without one. Either that or talk someone into tagging along.
