Re: lapua brass?
I think if your goal is a world record group at 1K then 2.8 grains differance is unacceptable. If your goal is .5 to 1.0 MOA at 1K I think you ought to do just fine.
Any time you want better than .5 MOA at 1K, you want EVERYTHING to be the same.
Long range shooting is a process that ends with a result. Once you start to focus on the result (where the shot goes, how big the group is, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.