What you're doing is basically a short range ladder test, I've been doing it for years because my range length is limited. It works fine to get close to right and does it quickly with minimum component waste, that's all anyone can expect from initial load testing. As you suggest, now it's time to start working in detail from 58 to 59 gr.
I've just used the same load others used in my match rifles. All the barrels for the same cartridge shot good enough to win matches with the same load. About 1/3 MOA at 300, 1/2 MOA at 600 and 3/4 MOA at 1000; at worst. Half a dozen or more .308 Win. barrels and four 30 caliber magnum barrels. I never worked up a load for each new barrel. Only once did I work up a load; a new Sierra bullet was introduced and I was part of a group developing loads for it.
I'm convinced most folks do not test their loads nor evaluate the groups shot properly. First off, you gotta shoot at least 20 shots per group to have it be meaningful to at least 80% confidence all groups will be no larger. Second, accuracy you can count on is the largest group shot with a given load. A rifle that shoots 5 groups from 2 to 5 units of measurements is more accurate than one that shoots 5 groups from 1 to 6 units of measurements. The 20-shot composite of four 5-shot groups will be larger than the biggest single 5-shot group. Most important, whatever shooting skills one has will be added to the accuracy of the rifle and its ammo. Nobody shoots a rifle and its ammo as accurate as when the rifle's clamped in a free recoiling test fixture. All of which is why I belive there are dozens (hundreds? thousands?) of "most accurate" loads for a given bullet and cartridge combination.
Pretty much a ladder test but cut down too short. IMO do the same but 1/2 gr increments two of each so you can do the test twice. Load them .02 off the rifling if your mag allows. Otherwise use saami length. Then shoot it at the longest range you can manage preferably 300 yrds or better.
Then you should have a good idea what nodes to use. Do a seating test and fine tuning with powder.
ACCURACY has nothing to do with PRECISION.
It takes only single shots to define accuracy, which is what matters in long range hunting.
1/2 moa of grouping, -somewhere on paper, no matter the number of shots, won't help a hunter one bit.
1/2moa of accuracy,, cold bore,, now this is a different matter.
Yes, but you have a chicken and the egg situation here. I don't care a bit if I can drop the first round of the day into a certain spot at 500yds (or any given yardage). The first shot is terribly important, but so are the following rounds.
I want the first ten shots hitting that spot so I have reasonable confidence in a follow up shot should said critter decide to run and I have to feed him more lead for breakfast. It's happened to me more than once where a 1 pill diet isn't enough and as such a rifle only capable of 1 good shot is simply a crow bar to me.