Wow, we sure don't have to worry about the quality of the barrel !!! I have no doubt the Lapua brass will do the trick. It is a shame that such measures have to be taken to get quality brass, but sometimes it does. I use alot of Win. brass, but they have cranked out some bad stuff lately. I found out last summer that I was getting better groups with Vietnam era LC brass in my AR than with with new Win brass & even the same brass once fired.
You might find a bullet that your barrel likes even more as you develop other loads, who knows? It appears a "one-holer" is in the works here.
Good shooting & good news.