I've had to use LRP instead of a Magnum primer many times in 300 WM and many receipts calling for a mag primers in 30 cal,25 and 243. I've seen no difference.
I have 3 Tikkas 300WM,308 Win & 243 Win. All shoot great out of the box, extremely smooth bolt & value priced.Expect 4-5 hundred for a scope. If you reload you can tame the 300WM down to 308 or 30-06 specs. If i could only have one it would be the Tikka in300WM. Shooting 180g Ammo.
If I could only have one scope magnification it would be 4x. I learned more about trajectory and accuracy when that was all I had was a straight 4x. Many years later all my rifles wear glasses. Leupold &Vortex.
I look at Manuals as a starting point. After selection of Powder & Bullet combo i go directly to looking at pressure & velocity, bolt lift & case observation to see how much powder i got to play with. Then the accuracy game is on.
Pressure first here too. Looking for bolt lift and case contition. Then start the hunt for accuracy eliminating obvious directions. 3 shot groups looking for improvements with powder charge compared to grouping's,I usually find more powder means tighter groups.