I think a .268 would be a good starting point. Right now with 110 Sierras I am using a .267. Case mouth on a loaded rd measures just under .270", and farther down the neck it is just under .271".
Well, not sure, I know I ran .268 with a hybrid.
Did not want to go into length, but on this batch of brass, I necked down with a Forster non bushing die with expander ball removed, then necked up a .242" carbide expander. Seating force felt like shit, then I annealed again before even firing it, went down to . 267 and it has been working extremely well going into 3rd firing. I anneal after each firing.
You can see I created my own train wreck and had to fix it.
Only once have I ever relied on one size bushing for a case, that was .286 for 6.5x47, worked for 6-7 barrels. So be prepared to experiment.
I'm using a custom honed Forster FL die with a .268 also, on
no turned Lapua brass.
I have some I turned and had to go down to a .266
This is on Lapua brass thats been sized down from 6.5
There's new brass coming out in 6x47 and guessing it would take less than .268