I've bought some 5 gal buckets of mixed unprocessed .223 brass.
In my case,it was nearly all crimped primers,(once fired mil)the majority Lake City,a fair amount of WC,and the rest mostly mongrel.A few IMI,PMC,etc.
Many folks don't bother to sort.They make ammo that meets their needs.
If you want to reduce variability,sort. If you are shooting all Lake City,or WC,
Your brass is not a problem.
55 gr bullets.There is a broad spectrum of quality in 55 gr mil spec bullets.Some don't shoot so good. I don't use 55's,myself,but my brother has been pleasantly surprised by the cheap,bulk Hornadys.
Powder is a definite player in accuracy(but not so much as bullets)
Varget,IMO,is a very sweet spot for 69 gr MK's. Not so much for 55's.
There are a number of good 55 gr bullet powders. H335 is one of the favorites.If you use H-335 with 55 gr bullets,you can rest easy that you have a very good combination.Its not the only choice,but its not wrong.Varget is a little slow.
While not the only primer,the CCI military grade primer costs a bit more,but resists slamfires.
Use a universal decapper (Lee) to decap. Clean your brass. De-crimp,size,trim,and neck chamfer your brass,inside and out. (lightly)
De-lube them.Corn cob works.
It does not hurt to run a brush through the necks.
If you have trimmed your brass to uniform length,and if your bullets have a cannelure,a light crimp with a Lee factory crimp die will resist bullet setback and may provide more consistant ignition.
Most seater dies have a buily in roll crimp which can cause you problems..You can defeat it from your process by backing theseater die off the shelholder 1/2 turn,ot the thickness of a penny or a washer..whatever you can do consistently.Re-adjust your seating stem for LOA.
This process will get you 200 yd ammo,easy.
Of course,you need a 200 yd barrel and a 200 yd shooter.