I was working up a load for mine this afternoon. 160 grain barnes, 77 grains reloader22, CCI 450s, 2275 fps. Shot right at .5". My original load was a 140gr. Accubond with 80gr. Reloader 22, 2590 fps. .35 inch group
As mentioned, "What are you trying to do with this gun? Deer at 100yds or elk at 800yds? It makes a difference on what you want to do. Let us know and we will try to help."
I picked one up second hand, initially to rebarrel into a 300 RUM, but figured I would give it a try first with some factory stuff. Just happened to catch some Federal 150gr loads on sale from Midway and picked up a couple of boxes. First shots through a clean barrel went under 1/2" at 200yds, and still does it with those loads. So I picked up 15 more boxes.
That said, those were loaded with the 150gr Nosler Solid Base and they get an honest 3250 from the 26" barrel on my rifle. I have since worked a little with some 160'ish grain stuff but have yet to find anything which groups as well as the factory stuff does. Since I already have an awesome shooting standard 7mag, I figured I would drop it's loads down to 140grs and bring the STW up to the 160's.
For powders, I was looking at stuff that I could get at least 3000fps from. This usually ended up being the slower burning powders. I just never got time to really narrow it down.
Depending on just exactly what you want to get from yours, and how your going to use it, will depend on the bullet weights and powders used. Just remember that any standard cup and core bullet running out the barrel at 3000fps and up is going to be fairly destructive at close up shots, but will do wonderful at long ranges. The opposite will be true of some of the premium bullets, where they will hold together too good at some of the longer ranges and not expand as readily.
Good luck and if you get time post up some more info on your rig and what your specifically after, powders and bullets you have, and that will help out some.
If you are punching paper try the Berger 150 gr VLD. If your barrel has enough twist shoot the 168 gr VLD for less wind deflection. If you haven't shot at 1000 yds before the wind is what rules your accuracy. That is why the long range shooters will go for the 30 calibers using 210+gr bullets or the big, 180 gr VLD's, for 7mm's. For the 180 gr 7mm's you will need a 9 twist barrel. In a 10 mph side wind the 150 gr bullet at 3200 fps will move sideways 70" and the 180 gr at 2850 fps will move 60".
For bullets, as already suggested check the twist in your rifle, your going to need the heavier 160gr bullets and up if they will stabilize. Berger would be my first choice followed by Hornady then Sierra.
For powders I would start with something in the H-1000 range or slower.
For 1K your going to need to prep your cases pretty well for uniformity. I was lucky enough when I got mine to find a decent supply of Winchester cases which have shown better load to load consistency than the Federals I got as factory ammo. Not that the Federal won't shoot good groups with handloads, just that they seem to be softer and more easily shotup than the Winchester stuff even keeping with standard loads. Depending on what your shooting this could also be an issue, so keep an eye on them.
The hardest part will be getting the LR Mag primers. I haven't seen many on the shelves as of late, and especially the Match grade Federals which most LR shooters use. Not saying others won't work but the Federals were the ticket when I was shooting out that far for consistency.
Also as mentioned the wind will be your biggest enemy followed closely by mirage. The high power scopes are wonderful but the mirage will eat your lunch at much more than 18X, even with the top end scopes.
I wished I could offer more, but I hunt with mine and I set 600 as the max range I would be shooting and for that the 160 range bullets will all work fine. I figured anything further than that I would walk up a little closer, or wait for another day.
Haven't loaded the STW but have lots of experience with the 7RM
I would try the Berger 180 VLD with R25 first. If that doesn't work then the 168 VLD. Other powders to try are VV165-170, US869, H100v, Ram Shot magnum and a few others.
Sierra Match King, Hornaday A-Max and several other good target bullets are available, but I like the Bergers as they are a good hunting bullet as well as for target.
My buddies load is:
150 gr Nos BT
75.5 gr RL22
Fed Mag Match primers
3250 fps out of his custom gun.
A relatively mild load that his gun likes to shoot. He has no need for more speed with the hunting he does out to 900 yards.