Brass weight is a crude measurement, not directly related to shooting small groups. Don't weigh it, just use same brand brass, with the same headstamp. The important measurement is the case capacity, and any decent brass will have consistent case capacity within the brand (Federal, Lapua, Norma, Nosler, Remington, Winchester, Barnes, other top brands). They will all have different case capacity compared to each other, though, so pick one and stay with it. Most shooters will use only their one chosen brand of brass.