LC brass is generally pretty good.
Almost all 7.62mm military brass is heavier than .308 commercial cases. Eight grains of brass has the same volume as One grain of powder. You must weigh your brass after separating it by headstamp, including the year of manufacture. Look for average weight, and consistency. You might find a good lot with a small spread. Generally loads in military brass hold about two grains less powder tham commercial.
I put different loads up in separate headstamped brass to give a visual difference, and work up loads specifically for that case.
Not .243, but I have converted cases to 7mm08. As I was looking for extra accuracy, I neck-turned the cases. I'm not sure how to handle the conversion to .243.