I run .3 or .5 grain charge increments, 2 groups of 5 per charge, 5 charges total. That is 50 rounds. That gives me a chrono of ten rounds per charge and I get two 5 shot group size references. I do that at max mag length. The second highest charge is book max and highest is over book.
Then, sometimes, I do it with 10-15 thou more jump which is another 50 rounds. That tells me what I need to know. At most, I might take the top 2 or 3 loads and compare them again in the same way if they are all close or I had a bad single 5 shot group. After that, if I have load, I shoot it till it wont shoot.
I have pretty much settled on CCI BR Small rifle primers and Fed Match Large rifle primers so I dont tune for primers. If I change powder or bullet I do the 50 round test again.
New powders and/or bullets are a new load. If I have great results with max mag length, I may not do the 10-15 thou extra jump test...that is ususually when I want to use a particular bullet/powder combo and want to see if I can tweak it because mag length left me wanting more.