Just built 300 WSM 1000 yard gun, had one day after break in to work loads before match. Tried something that worked well. Knew components H4350 powder and 190 JLK bullet, F210 primer to try. Only issue as load. Load range was 58-61 grains. Loaded cases (one each) in .3gr increments. Zeroed at 410 yards at bottom of large target with lowest charge. Shot and chrono'd one round at a time starting with lowest. Marked on paper at bench exact bullet location. About 3 shots into it, 4 bullets clustered, then 3-4 shots later 6 bullets (each different charge) went into 1 1/2inches. These clusters are supposed to be "sweet spots" for your barrel and load. Due to short time and not able to do further testing, just split the diff between top and bottom of top cluster. That gave me about 2900 FPS with load not near top on pressure but accurate. At match next day shot 3 sub 8" ten shot groups at 1000. Further testing will work on seating depth and fine tuning. But great way to find sweet spot to start with. 15 rds versus 15-5 shot groups.
I've been using this method for several years and it's always worked great for me. I don't shoot at 400 yards for the test, I stick to 100 yards but the technique still works. One trip to the test site and the load data is known, easy as pie.
Shot the test at old Remington Range at Rob Ritchies house in the drizzle rain. Just as simple as I laid out. Nothing fancy. Thought about doing it at 100, but figured it was key to be able to plot each round on paper to see which one went where. Used pure white target with magic marker one inch dot at bottom. Easy to see bullet impacts. Figured distances up might be too close to clearly differentiate between shots at 100. That is why used 400 yds. Each round went up about 3/4-1 1/2 inches except when they started to cluster. You can look at shot string up, clusters and MV and sweet spots are easy to see. Then it just becomes matter of fine tuning. Figured you can do this with each powder and see what the gun likes. I know for me to find a range of 1.1 grains spread for a sweet spot, I will take that. Also ran out of up on target and loaded rounds. Next time I am going to go up a little more on powder, absolutely no signs of pressure and I think I can raise it up to 3000fps with the JLK 190. Got to do it before the Nationals Labor Day in NC.