To cover a few things
For the most part the 7mm mag’s tend to like the 160s , floating any ware from the high 50s to mid 60s. Somewhere in this range you will find a forgiving accurate bullet. You should end up with a load that should be consistent and user friendly with wind calls and corrections.
Once you have gotten past the first 20 rounds which mattering on the gun, barrel manufacture will dictate the importance as to how to get through those first 20, and then life goes on.
Examples of this would be
My 338 LM Barrett
Was to run 5 down the tube and then clean, repeat this step and run another 20 rounds and clean again. Then run’er until the accuracy shows signs of falling off. This will be around 400 – 500 rounds give or take. But note after a good cleaning it will take another 10-20 to get back to what it’s capable and that being a consistent ½ to ¼ moa rifle hitting intended targets well past 1760 yards
My 260 with a Brux barrel (a sweet heart) or any manufactured rifle off the shelf as well would have a patch or two ran down until clear. This is done every shot for the first 5 to 10 rounds watching the rifling marks in the patch, you will see if there is any snags or burrs in the rifling by the dirt residue and if cleaned every shot you should see the dirty snag disappear as the rifling is burnished in and gone, the ruff areas become smooth and the pit marks tend to be filled. This leads to consistency, accuracy as well as a barrel that cleans fast when needed and fouls out in a longer period time shooting.
Then life goes on, most guns and they all tend to have their own personality will tend to shoot good at this point but yet the groups will tend to be good one day and another start to open up and possibly even have pressure signs starting to show. From what I have seen it takes a good 100 rounds to break in a barrel, we tend to call this a barrel ramping up, settling in or a barrel that burnished in. Velocities slowly tend to rise as well as the feeling that one needs to clean the barrel do to possibly be fouled but it’s all about the barrel settling in. Re-tweaking a load some or trying a factory load that was marginal prior may be the load that the gun wants to shoot at this point and shoot well.
So the point is shoot what is fairly accurate, get some trigger time on the gun and then after hitting the 100 round mark, try a few different loads and see if you can turn your 1 moa rifle into a ½ to ¼” moa gun.
After cleaning a gun throw some foulers down the barrel, some may only take a few shots and some may require 10 to 20 rounds to settle back in and be spot on. Many folks get confused when after cleaning a gun and going back to the range they can’t hit as tight as before. Then folks start to get frustrated and slide down hill fast versus keeping an open mind and watching the groups come back after shooting some. After that when all is well shoot and shoot some more. As I stated mine don’t get touched until around 400-500 rounds you will know when it’s ready. Everyone has a different idea as to when to clean and how, this is just mine and many also do the same
There are a lot of variables that makes a gun shoot well, mechanical and operational and even the best shooters can have a ruff day so don’t beat your self up.
Your groups watch your verticals the tighter your vertical dispersion the better. The windage (lefts and rights) can be caused by cross winds down range or a tight grip with your trigger hand as well as not coming straight back with the trigger then holding until the shot recoil is complete.
If you know the shot is perfect without a doubt with the wind and shot sequence and you have repeating targets of the same load showing a horizontal string then and only then I would consider a different powder choice, otherwise all powder adjustments and variances will show up with a vertical report.
Also before throwing in the towel on a load especially now after you have been shooting this some, check and torque your action screws, base screws and scope ring screws.
Hang a plumb line out at a 100 yards or even closer and check to see that your scope reticule is true and square with the plumb line after checking that your gun is level. Once you know that is on add a scope or rifle level or just take a small level bubble and mount it below your scope. If you use a small level bubble in a tube, roll it and watch what the bubbles does, you may even have to mark it because it’s amazing how many of them aren’t perfect either. The bubble reference is nice to have to check when you’re shooting out at 300- 400 yards and beyond it eliminates any possibility of canting your gun and causing left or right hits
Again I would hang in the 160 gr range so 155 to 165 find what she likes (use 5 round groups) this weeds out bad shots better and if anything set up multiple targets and rotate your shots one brand or grain one on one target and another on its own, but shoot one shot with the 154 gr then one with the 160 and then one with the 165 then back to the 154 and again for an example. This keeps the playing field fair as far as weather conditions, barrel warm up and operator fatigue.
Once you find a load that holds tight vertical groups check it against what came in second again just to prove to yourself that the results are the ammo and not influenced by the operator
Hope some of this is of use
Good luck
happens!