Shooter <<---- #1 far and away
Load tuned to barrel harmonics
Watched my daughter's BF shoot PPU Factory ammo through her Marlin XL-7 in 7mm-08. Five shots, he *might* have been 2 MOA. As he got up from the table, he muttered, "cheap gun." Sure was a cheap gun. I think I bought it for $249 from CDNN. Had a Japanese made 4X Simmons for a scope that I bought used for $35.
She sat down, put the next five from the same box in the X, all inside a nickel. I've seen her shoot that well many times, it wasn't luck.
assuming a decent shooter and a halfway quality rifle with everything tight and in it's place...
1. bullet- bore compatibility- if your pipe doesn't like the pill in the first powder or two tried then switch
2. powder- decent burn rate for the application
3. case- uniform weight and decent condition
4. neck uniformity- keep the length similar- you can actually see it on a strain gauge when you have short and long cases in the mix together
5. primer- enough to do the job- I'd rather over-ignite a bit as things get going slower in cold weather
6. jump- jump is bad in short range match situations but many bullets hunters toss at game actually like a good bit of it
Most of my attention these days is toward consistent neck tension at low as I can get away with.
My operating theory of reloading is that, if I find a temperature stable powder that fills the case without compression, burns completely in the length of the barrel, I will get SDs in single digits with consistent neck tension. Then I can test seating depths with my chosen projectile which nearly always is within a gnats eyelash of the lands. Many bullets will be constrained by magazine length or are "varmint" bullets that will never reach the lands.
Quickload helps select powders from Hodgdon extreme, Vhita Vuori and a few of the newer Bufors from Alliant. Alliant Swiss Nitrocheme are also excellent. I have had success with Precision (SO-62).
Adam MacDonald's kernel counter is key to getting charge consistency. If you don't think this matters, this is the easiest variable to test.
Walt Berger suggests testing at 300 yards. I test at 300 and 600 (target cameras).
Just like Secant ogive bullets are less sensitive to seating depth than Tangent ogive bullets. A recent corollary to my reloading theory is that HBN coated bullets are less sensitive to seating depth choice than naked bullets..
When do I choose to call a load settled? I define accuracy as 3 inch groups at 600 yards. I have a few rifles that will shoot 2 inch groups there. My AR-15 .224 Valkyrie (factory CMMG Endeavor barrel) managed 0.442 at 300 yards (six round group) but I am still struggling with both it and a .223 Wylde upper at 600 yards ( 6 inch is typical). That is a challenge I enjoy.