Another thing to consider besides what scope is what kind of scope base. This is especially true when setting up Magnum rifles because one of the biggest reasons for these weapons is the range potential they offer.
On any long range Magnum rifle you should seriously consider a 20 MOA base. This will get you sighted in at much longer ranges without running out of elevation adjustment. Most "hunting" style scopes have a limited amount of elevation adjustment. Much less than a Magnum rifle is capable of shooting. By going to a scope base with a 20 MOA downward slant you automatically add 20 MOA to your elevation adjustment by taking away 20 MOA of downward adjustment you don't need, and giving you another 20 MOA of upward adjustment you can use to reach out without using holdover, or even Mil-Dots, which most hunting style scopes don't provide anyway.
For example I have a 20 MOA base on my Kimber 8400 Police Tactical in .300 Win. Mag. I scoped it with a Bushnell 3200 Elite Tactical 40 MM scope which I like a lot because of it's clarity and repeatability.
This gun has the capability of shooting at 1,000 yards like an AR has at 100. The Bushnell 3200 Elite Tactical has a total of 40 MOA adjustment of elevation, (20 MOA either side of center). By going to a 20 MOA base I get an additional 20 MOA of upward adjustment for a total of 40 MOA. This will give me the ability to hold dead on out to 1,300 yards pushing a 208 grain Hornady A-Max bullet out the muzzle at 2,850 FPS, which a .300 Win. Mag. can easily accomplish. At that distance a total of 36.7 MOA is required. Add in the Mil-Dots, (4), and it can go well beyond that.
So you can see how much additional range you are capable of getting by going to a base of this type. The whole purpose of using these Magnum calibers is the range potential they offer. By going to the correct type of base, you can extract this range capability far more easily, and without "guessing", which will all but certainly guarantee a miss at long range regardless of the conditions you're shooting in.