The only thing that I would really emphasis from what all the others have said is be sure to get a fast twist and shoot the heaviest bullets you can. You need to retain that energy. Also be sure to run your load across a chrony. You really want to know how fast it is going so you can keep it super sonic at the limit of the range you are shooting. My limit for hunting is 400 yards with a 260 Rem on deer. And that is only if the conditions are perfect. 300 yards most of the time. As a brief aside Hi guys. Slim
I have a XP-100 in 300 Dakota that I hope one day to shoot an Elk with and plan on a Mulie this fall. I shoot 185gr Berger's and there running 2900fps or so from a 16.5" barrel. I'm in the process of working the load I'm going to hunt with now. I also have an XP in 7.21 Lazzeroni that I shoot 168gr Berger's at 2850fps also from a 16.5" barrel. I took a Buck Lope at 440yd's last year with it. I shoot the 3x12 Burris with Bal Plex reticle and I would shoot out to 600yd's with the right condition's. Me and Ernie and sscoyote went to the range in Casper last year and I shot from my bipod prone 3 shots at 600yd's that measured 6.75 inches. These short rifles are capable of longer distances than most people would think. There not that far off from rifle velocities with the round's mentioned above. Good luck with whatever you decide, ask a lot of question's and enjoy the insanity it's an awesome hobby.
One issue that is important for all LR shooting but may be more noticeable using specialty handguns is impact velocity. The accuracy of specialty handguns can give one the ability to out shoot the bullets ability to perform well. Each bullet has a minimum velocity that the manufacturer has given and I would encourage to follow those guidelines. If you are shooting paper, steel, or prairie dogs it is not an issue what the impact velocity is, but game is different.
My primary elk SP is a 325 WSM, it is the HSP 2000P single shot ( looks like a XP). My back up is a 300 WSM HSP. Both wear 3.5X15 NXS withe the NPR-1 reticle. With the brake i can get just about full field of view with these scopes. I have the 5.5X22 NXS on a few other SP's and they work great. The 325 sends a 180 gr BT out the end of the barrel (15" + brake) at just over 2750 FPS and the 300 WSM sends the 165 BT at over 2830 FPS. I hope to use them on an over the counter tag ( depredation hunt) this december and hopefully next season on a draw tag in AZ.
I agree with what the others are saying.
My 7 SAUM has a 17 inch barrel with Defensive Edge brake and I drive 140's to just over 3K fps, which is about what you will do with a 7 WSM.
For the larger game such as Elk, I would stick with the heavier bullets like has been suggested.
My gun weighs in around 10 pounds +/- without bipod.
My .338 WSM is more portable with a 15 inch barrel (about the same weight) and will push 200 grain AB's to 2725 fps and 180's to 2850 fps. I would feel safe shooting an Elk out to 275 yards or so, maybe 300 max (due to bullet performance).
Lately for long range (400 - 800 yards or beyond) I am going with longer barrels of at least 20 inches. It's the only way I know to keep my velocity up and wind deflection down.
I'm currently having my xp 100 in 7 Dakota rebarreled with a 25 inch tube to send 180 Bergers at 2950 or more.
I might be able to do it with a 23 inch barrel but will start at 25 (can cut but can't stretch it).
I think any scope of your liking that will max out at 15-20X will be more than adequate.