Personally I wouldn't do it. Even if it is legal, these days they open almost everything going international, so I wouldn't want to have brass being opened by anyone related to the current admin. I lived in Japan for 5 years and I feel sorry for anyone in foreign countries, but I'm up to my armpits and trying to fend off the 'gators in America. I don't even want to pay hazmat for powders and primers. Can we trust we won't be put on some list for transporting powder or primers? I just heard the President claims how deadly 9mm bullets are and there's a bill to register anything as deadly as 9mm that can puncture a lung! Can you imagine that?
I'm sure there's nothing to worry about, but I'm more sure for you than I am for me.
And I should add, I do have a lot of experience with international shipping, and Australia is always one of the more difficult. I see the OP is in NZ, and I don't know too much about NZ, but AU is one of those upside down thinking countries in regard to firearms. Can you purchase directly from Lapua? I would think it best to keep America out of it if you can...just sayin'...