Re: How many rounds does it take.
I tried the shoot one, clean, shoot one, clean, ritual with my L-W SS .260 barrel. There was no detectable copper after the seventh shot, so I no longer bother doing such activities with a honed premium bore. Most factory bores aren't honed and can probably profit from more frequent than average cleaning during the first 100-200rd
There is some reasonable argument that the throating process leaves some sharper edges that are better after some wear, but I don't think there's much point to deliberately going after such.
I would give any new premium barrel about 100rd before trying to do definitive load development. If an accuracy node is a moving target early on in the barrel's life, it should have settled down by then. As said above, the rest of the rifle can probabably use some working in, too.
Greg