Here's what I did to work up a load in my .300 win mag if you're interested; I shoot 208 ELD-Ms as well but I use Vihta Vuori N560 and get great results.
My gun is a Tikka T3 rebarreled with a Lothar Walther 32" Super Palma 10" twist running a SAAMI chamber and throat. Even with MDT's 3.56" metal mags, my action limits me to 3.426" COL so I have to jump the bullets at least 90 thou. I look for one or more accuracy nodes that corresponds with charge weight(s) and load / test those afterwards.
Basically I pick a charge weight range and load test rounds in increments of .2 gr from the starting charge to what I conclude might be a max / upper end charge.
Example: 70.1 70.3 70.5 70.7 70.9 71.1 71.3 71.5
I try to load at least 3 rounds per charge weight; more is better and you'll see why in a pic below.
Example: 3 x 70.1, 3 x 70.3 etc etc
I then pick a decent distance (at least 400m if I can) to set up a large poster board with a decent aiming mark. Maintaining the same point of aim and exercising excellent principles of marksmanship throughout is critical for this. I don't worry about the wind but calm and bright conditions are ideal. If you have a spotting scope and a buddy to keep track of where shots go, you can plot where your rounds went and when. I tend to use different colours of permanent marker and colour the tips of my bullets to represent corresponding charge weights. The marker on the bullet transmits to cardboard and poster board quite well if you're shooting alone and need feedback for where your rounds went. I also have a wireless camera system to record shots as a backup.
I shoot the test rounds in following order:
Lowest to Highest - checking for pressure signs as I go and stopping at what my gun / handloads hint at as being upper end.
Highest to Lowest
Lowest to Highest
Once that's done, you could have something that resembles this:
If you look at shots
1-8, you'd think that shots
2 and 3 are an accuracy node or that
4,5 and 6 show good potential because there is very little vertical dispersion. I got away from shooting 1 charge ladder because there is always the potential for shooter error to skew results. Thus, I shoot at least 3 charge ladders at the same point of aim and it gives me more useful data on what my loads / gun can perform like.
With that in mind, 71.3gr is what I settled on in this case.
I then load at least 10 rds of each charge weight that may be an accuracy node and shoot them for a group at at least 400m over chronograph / magnetospeed to collect velocity data. In my case, my load gave me and SD of 7.5 and AVG velocity of 3035; not too shabby. I don't have a pic handy but 10 rds at 400m gave me about 2 1/4" group center to center (roughly 1/2 MOA.)
I basically combined some ideas from OCW and other ladder test methods and use this one a lot because it minimizes the rounds I need to fire while maximizing the data I can collect to better decide on a good load based on what my goal is (ie low SDs and an as little vertical dispersion as possible while staying at least sub MOA but potential for sub-sub MOA.)
Now if you have to start low and want to work up towards a much higher max / upper end, I basically do the same thing but in separate sessions (starting at the lowest end of course.)
Example: 70.1 - 71.5 one day and then 71.7 - 73.1 another day
Try to keep the weather consistent / timeframe narrow; don't shoot these tests months apart or one on a cold day and one on a warm day.
As mentioned above, you could space out your charge increments depending on your particular case volume. One thing to keep in mind is that there is always the possibility of narrow accuracy nodes and larger charge increments could mask / hide these. No combination of powder / components / barrels will 100% perform predictably and/or consistently. I also will suggest that as you get closer to max / possible upper end to narrow your charge jumps to avoid catastrophic surprises (increments of .2gr instead of .5gr etc.)
Hope this helps.
