I was never in the rabbit hole until I started reading on forums. When I started reloading I only used the brass from which ever brand of ammo was bought. At that time I only reloaded/shot 2 cartridges (1 per rifle)(264wm & 270win). I never gave any thought about using any other brass? I haven't tried mixed brass for 1 load for 1 gun, but I might have a thought about that? Forgoing case weight and just check case volume for testing before moving forward. What I do on every reload is fl size (works for me) on ba's and AR's. With a fair amount of brass from different mfgs I do separate. Most brass I buy is due from availability. I'm still using super-x brass from the late 70s and early 80s in my 264wm that's been fired and fl sized well over 10 times. I can't swear by 1 particular brand.