New vs Old Brass

[Bassfish1952]

You've got 1000 of pretty uniform, 6 Arc brass, so roger, will take you a few years to go all the way through it.
Lots of shooters cycle fresh brass once with any fire-forming load, then concentrate on using the fired brass b/c it's more conformed to their particular rifle/chamber.  For myself, I go to "some" degree of uniformity but not to the n-th degree.  So I've got a lot of fresh starline (but not 1K!) so develop a consistent load in that fresh brass... once it gets all the way through I will re-formulate for the 1x-fired. 

What I'm finding in lots of calibers when keeping everything else the same (and I mean Everything) except the  once (or 2x or whatever)-fired vs fresh brass, is fresh brass loses some energy to the chamber-forming, so shoots a bit slower than the fire-formed brass (less available energy to push the bullet).  (The factory shoulder/oal is pretty much always shorter than both your chamber and what you will re-size it to, so it will take some amount of energy that first time to "blow forward" the shoulder to where it will be ever after. )  But for a 1000 pieces you will undoubtedly change over something in the powder, powder lot etc, or primer lot, or bullet lot, etc, so might as well shoot that thousand first, then worry about adapting your load to all the once-fired.

I have some 308 brass from various mfrs, and several lots of Lake city of various years.  A couple of them shoot pretty much alike, but that's been the exception rather than the rule.  It has mostly to do with the interior volume of the case, and thus the pressure curve that the powder will generate.  If by some chance you have 2 types of brass with identical (or very very close) chamber interior volumes, then they will likely exhibit the same or very very similar MVs and pressure curves.  But in the vast majority of cases (lol!) that won't be, so the different cases will show different MVs and pressure curves.  There's probably 10 or 20 different ways/dimensional parts to a brass case that can cause its interior volume to vary.  So we keep the mfr, times-fired (I call them 0, 1x, 2x, etc) and maybe even the rifle they go in, separated in little sandwich bags or plastic bins (or whatever), and label them to avoid mixing them up and causing us some surprise at the range or in the field... I have 2 brands of 308 brass, that for everything else the same, shoots 150 fps different from each other... so the one was over-pressure!  shocked me! (no kabooms or anything but definitely a surprise when I saw the MV numbers).

I get involved in the extra noise and forget where I am headed sometimes. I decided back during the shortage that having extra never hurts .  My one concern was powder and primers but after posts on here anything I buy will last past my effective expiration date so I stocked up on Brass bought enough bullets , powder and primers to learn what loads I want to shoot. I will complete my buying then . Plan is 1000 brass and powder , primers and bullets to match once I know. While I can I want to stock up and avoid any shortages later. To me the most important is getting a couple of good loads that shoot in my rifle and then duplicate , duplicate , duplicate .