Not sure it really matters, unless you're shooting benchrest matches.
Once you find the bullet, powder charge and primer that your rifle appreciates, you'll find shooting mixed brass doesn't seem to affect group size, at least that's been my experience.
For instance - I have found that 23.0 grains of Varget with a 77 grain Sierra HPBT-Match bullet with a Remington 7 1/2 primer will shoot 5-shot groups under 0.5" at 100 yards indoors, but go heavier or lighter with Varget and you are at an inch and larger - change the primer to Fed 205M and the group opens up to an inch. This with an AR, 1:7 twist, 16.5" barrel, 32X scope and JP trigger.
Using CFE223 powder, 27.0 grains with Fed 205M primer and 52 grain Berger target bullet, I shoot 0.3" - change primer to Rem 71/2 and group goes to an inch, V V133 power, 24.5 grains I get 0.4" with Fed 205M, but change primer to Rem 71/2, group goes to 0.7". This with a Rem 700, trued action, 2 oz trigger, 32X scope and 24" match barrel, 1:12 twist and 52 grain Berger target bullet.
Those groups are consistent - not shot once in a while when the moon is just right etc.
I'm kind of anal with brass, as I uniform the flash hole and primer pocket on all my cases - 223/556 - makes me feel good for some reason.
I spend more time and money purchasing reloading components, vehicle gas, targets etc going back and forth to the indoor firing range, lugging my rests etc to find that load to produce little bug hole groups and then go out and miss a fat prairie dog sunning himself at 200 to 300 yards - well, that just means my rifle, ammo and accessories were up to the task but the jerk behind the trigger misjudged the wind, mishandled the rifle or some other bonehead mistake and that prairie dog will live to see another sunrise.
Guys I shoot with - their good loads shoot from an 3/4" to 2" at 100 yards consistently and they seem to do just fine in the varmint killing grounds and the big game fields, so what's the point of all this?