A few of you know that I am a former 1K shooter. What most all of you do not know is that I started out as a M-1 Grand Class Palma shooter. I was average with my 1943 Garand. I started hanging out with the "real match" shooters. BR guys, 1K'ers, 50 cal Milers, and Palma guys that took the "sport" seriously. Now a really long story as condensed as I can.
I was average in my class. I wanted to make better ammo to compete with the "big boys", that lead me to start asking aobut case prep and other advanced reloading techniques. The amount of information I had to digest in a short time was rather huge. Some of it was pure BS.
I did get a bunch of really good, useful information from all these guys. Especially the things that make your brass more consistent. My groups off the sand bags went from around 2.5" to just under 0.750" edge to edge at 100 yards. For those that must hear the C to C; that would be 0.342" from a 1943 M-1 Garand. That is a vast improvement in my log books. So, yes, I believe in case prep. No matte the brass' head stamp.
From all of the things I was told to do to that first 100 pieces of brass.. I am not proud of what I did to that first set of brass. I had to completely trash that set and went to another 100 pieces and this is what I did to them. Trimmed to uniform length, Reamed the necks for uniform thickness and concentricity, uniformed the pocket depth, then drilled the flash hole with a jig for consistent center and uniform diameter (0.085"). Then weighed the brass for uniform weight. I found that I had to prep most all of my supply of 30-06 brass in my father's collection. He was happy. He got his brass prepped and he did not have to do it.
I ran an experiment on what made the biggest difference in ES, SD, and such. what steps made the biggest difference. Here are the results directly from my log books.
#1 is neck uniformity (length, concentricity, and thickness)
#2 is uniform weight of case (the less the variation if combustion chamber the more uniform the speed down the barrel)
#3, is uniform neck hardness (annealing)
#4, is uniform ignition (flash hole uniform diameter and centered)
#5, is uniform primer depth
from here it is all reloading uniformity
#6, is uniform powder charge
#7, is uniform projo weight
#8 is uniform projo shape
The improvement from primer pocket depth uniformity, flash hole uniformity and centering is seen better the farther you go out. At 500 yards you see about a ½" to 2" improvement depending on diameter of the slug. At 800 you can start seeing improved/more consistent grouping. At 1,000 yards your groups should be at least 30% smaller. At 1,500 yards I saw all of my rounds not only on paper but nearly all were in the black. 18" black (7 ring to bullseye). I saw less and less errant flyers. I saw less and less SD's (average 8 or 10 shot group was just under 8 FPS) best SD's were seen at being 4 FPS.
I apologize for taking so much space to say what I found out 25 years ago. This was seen in both Palma and 1K, and 1,500 yard competitions. I did not see a need to distinguish since they were pretty much uniform/linear improvement.