Playing with my AR15 in 300AAC, I use the Lee C312-155-2R from a 6 cavity and like the results. Now I have time to fine tune a little. I made a sample run from just a single cavity of my 6 cavity mold to remove the potential that the cavities are not identical. I think I buy into the idea of casting from single cavity for best accuracy potential. I was actually impressed with how fast it went. Anyway, I weighed the 20 to 25 sample bullets and found a median weight around 149.7gr. I used a maximum acceptable variance of +-.3gr which caused me to cull 5 bullets. My absolute heaviest bullet was just over 150.0gr and the lightest was 149.3. How tight a tolerance makes a practical difference?