Well no one has brought this angle so let me give it a go. Sometimes if you really want to study a rifle as it was used and not just shoot while eating your banana, there is no substitute for surplus.
Case 1
Back many years ago when I was a young lad, and WWII ammunition was still around, I read the following:
1) US WWII M2 ball was "Smokey" and had flash problems at night
2) 303 British had similar issues with Flash at night
3) German SS and SME ammunition did not.
So I tested surplus ammo which was available at dusk, at night and in day to see if I could verify the above. Some I did , some I did not. Also caused my father some stress as I blammed away outside of his house at night, setting up cameras if front of the guns to take pictures, etc.
You cannot do that with new reloads.
Case 2
Some years later I got interested in UK regulated .303 service rifles, that is rifles set up for SR(b). Guess what, they were set up for MK VII rounds.
So I tested rifles' with these rounds, many different lots, and found out a lot of interesting things, from reading the 1929 handbook and checking. Lots to know on this archaic topic.
You cannot do that with reloads, they do not make cordite, you cannot get the correct MK VII bullets and interwar crimping is not something you can replicate. And the rifles were set up to shoot that.
Case 3
So then 10 years ago I got interested in the generation 1 commonwealth 7.62 NATO target rifles.
To really see this operate as they were meant to, you need to shoot surplus ammo. They were set up to get the best accuracy out of C21, F4, L2A2, (with some DM41 thrown in) ball ammo. Learned a lot about the rounds, some in line with regular concepts, not so much. Some of the regular ball shot very well indeed, if there was a match between the barrel and the ammunition.
To shoot reloads would miss a lot of that history and the appreciation for these old target rifles.
Case 4
Swiss 300M shooting.
So I belong to a overseas swiss rifle club. Guess what we shoot in K31, Tanner, Hammerali rifles? It isn't reloads. It is GP11. To sit down and knock out a mid 90s score on the A 10 target at 300M is a feat and the 8.8 Lb rifles do it well for 6,000 to 8,000 rounds, some close to 10,000.
The steel cupro-nickel plated bullets, slow powder and very high neck tension all go to making these rifles shoot so well so long. Ang guess what...you do not clean them, yup, just grease the bore between sessions. An entire season with out cleaning with bore cleaners, nitro cleaners, copper removers or other stuff we in the US are used to.
reloads in such a rifle kind of miss the point. In most cases a rifles is part of a weapon system and the ammunition match is part of that system. You will learn things with careful study and experiment using surplus that you will not studying the Sierra reloading manual.
Final offering: Try shooting surplus .30 M1 and M72 bullets out of a worn but shiny M1903/ M1 barrel and compare it to reloads using Sierra 168 to 175 grain Matchking 7.62 bullets, same everything but the bullets. I bet you the M72 bullets groups beat the sierra groups. Hmm...wonder why...………. What can one learn from that?