I've always used RP brass with no problems. I buy virgin brass in bulk and load it over and over many times and it seems to last forever. I agree that you shouldn't use mixed headstamps and if your finicky you can sort by weight. I've tried sorting by weight but i've never seen an improvement in accuracy by doing this so i don't do it any more. Maybe i've been lucky but the RP brass i've used has been very uniform in weight. I've found that i get my best accuracy by juggling components and playing with seating depth more so than worrying about my cases.