Well now, I do have to concede that point about factory ammo. To be honest, I didn't even think of that because in center fire rifle ammo, I bet I have not bought 100 rounds of factory ammo in the last 50 years combined. I just aotomatically assume I am going to provide my own ammo. So you point is accepted and taken.
Brass..............only a problem if you want the head stamp to read "300 H&H"
I just run a 375 H&H through the die and bingo...got it. No problem at all.