I remember when I first got into 338 Lapua magnum loading, Tecrep at Sierra told me a bunch of loads for 338 Lap. I wrote them down, then he told me to make sure to only use Lapua brass, Norma was allright he said, but much less interior capacity, and something about the softness of it not working as well. I have found the same to be true of the 300Wm brass. I believe BH used to use Norma for 300 WM, then switched to their own BHA match.
just my experiences lead me to see Lapua has always been better for me.
Chris