Weighing brass is pretty much an exercise in futility (and consequently, so is weighing final assembled rounds). It might be an interesting mental exercise for hyper-consistent reloading, but it is pretty much pointless for normal humans
I have a single bag of unfired brass (Starline) for 45 acp that I have never opened. 95% of my pistol reloading brass is WWB collected over the years from my own store-bought ammo. 100% of my 308 reloading brass is Remington Core-Lokt also recycled from personal store-bought ammo. 100% of my 30-06 reloading brass is surplus Lake City bought from the CMP as actual ammo.