What I would like is some sort of proof/data that a certain step has made a measurable difference in accuracy. Right now I'm chasing the accuracy goal with my GAP-10 but I will be having a precision bolt gun built soon. Here goes...
I have been wondering the same thing for years, and have "chased the accuracy goal" in many ways with many reloading methods in many rifles. Here's my story. I started shooting service rifle matches with a buddy in 1990. The "accuracy goal" there is 1 MOA, or the size of the x-ring. My buddy did lots of case prep and weighed every charge by hand. I had very little time to practice or reload, so I bought a Dillon 550, set it up with Lee dies, and loaded everything progressive style. The only case prep I did was to remove primer crimps from LC brass, and trim it to correct length with the Lee trim tool in an electric hand drill. After awhile, my buddy and I were both shooting expert scores in matches. A couple of times, emergencies arose and I either had to borrow some of his ammo, or he had to borrow some of mine. On those occasions, we saw no obvious changes in our scores.
Derrick Martin of Accuracy Speaks built and test-shot my service rifle using my progressively-loaded ammo. In his hands, it reliably shot 1 MOA or better. Later, I got seduced by the idea of itty-bitty groups in bolt rifles. I started with a Savage Model 10, with a heavy barrel. With my mediocre abilities, I could reliably get it to shoot better than 1 MOA using Federal Gold Medal Match and my service rifle loads. But I wasn't getting those itty-bitty groups I wanted. So I sold the Savage, and bought a lightly-used Remington 700 built for Palma competition that had a good reputation for accuracy. My groups were a little better, but not much. So I started experimenting with each of the precision reloading steps you have identified, except turning case necks. I also experimented with different bullets, OAL and cases - except Lapua. My groups did not improve. So I sold the Palma rifle and bought an FN SPR with a 24" Obermeyer barrel from a 'Hide member who had been using it in tactical matches and reported that it shot 1/3 MOA with M118 ammo. The barrel had about 1200 rounds through it at the time, I think. I was excited to try it out, but in my hands, it shot about the same as the Palma rifle. I was a little frustrated.
Because it was what I had at the time, I took the FN to a wind-reading class in October. I used 200 rounds of an M118 clone handload consisting of 175 gr. Sierra MK bullets (pulled from surplus ammo), LC 63 brass, and 41.3 gr. of RL 15 over a Remington 91/2 primer. The handload was assembled full-progressive style on the Dillon, using a Lee FL sizing die, the stock Dillon powder measure, an RCBS competition seating die, and the Lee factory crimp die. I weighed powder charges 10 random times during the loading sequence, and found that the charges did not vary more than .1 grain from the nominal charge. At the class, we shot paper targets at 500 meters on one day, then shot steel targets the next day out to about 1200 meters. We had shooters on the line that were way better than I was, but we had some that were about the same as I or worse. Equipment-wise, the FN was the cheapest setup there, with possibly one or two exceptions. But I had no problem hitting the steel targets at all ranges, and my paper targets were middle-of-the-pack in size.
Still, I wanted smaller groups. So I signed up for the 'Hide marksmanship training, wondering if a change in technique might help. Along the way, I bought two more .308's, on the off-chance that maybe my problem was equipment-related. One is a Sako TRG-22 with a 20" factory barrel; the other is an M24 clone with a 24" Krieger barrel that was said to have been built by a military armorer. After trying a couple of things from Frank's training video (chiefly dealing with trigger manipulation and recoil management), I started getting what I call itty-bitty groups from the FN -- using my M118 clone progressive handload! I was intrigued, so I tried the same ammunition in the TRG-22. I got more itty-bitty groups. I took the M24 clone out last Saturday, but for reasons not important here, I had a less-than steady position. I still got what I call pretty good groups, using the same ammunition.
Not all my groups have been itty-bitty, and I have not shot for group size beyond 100 yards. Moreover, my itty-bitty groups may be huge by others' standards. But the fact that I could repeatedly shoot what I consider small groups indicates to me that larger groups were not likely due to the rifle or ammunition. For each rifle, the groups pictured below were the first two groups I shot. I typically struggle a bit after the first two groups, but with both the FN and the TRG-22, I have shot similar groups after firing strings of 20 or more rounds. Maybe altering my reloading methods or materials will result in better groups at distance. My next project will be to fire groups at longer distances to see how much improvement in ammunition is needed. But so far, but I have not been able to produce any measurable difference in my practical accuracy by using any of the reloading techniques you mentioned. My greatest advances have come from improving my shooting technique.
Here are the targets from the three rifles:
FN Target 1 (3 shots)
FN Target 2 (5 shots)
TRG Target 1 (3 shots)
TRG Target 2 (3 shots)
M24 Target 1 (3 shots)
M24 Target 2 (3 shots)
