I use Lapua Cases, for my match grade reloads. I weigh each case, check the highest and lowest weights for load density/ case capacity.
Lapua is one of the most constant I have found. That is the case to case in a lot. Lots can and very a great deal.
I do not use mix cased for matches, for the reasons stated above. Different cases and the very slight differences does make a difference in shot to shot accuracy. But I do have mixed case ammo for plinking. All Max loads in the manuals are still well below what case manufactures build their cases to with stand. The cases may not be the best but they are all made using and within certain safety specs.