The differences are exactly why I'm asking.
If 0.100" over the threads, then why is ~0.730" not enough?
It absolutely is. If you look up thunderbeasts' threading chart, they show 0.725 as min muzzle diameter for 5/8 threads.
I decided to have a collar put on mine because the Tikka factory barrel is only 0.630ish at around 22" and I wanted a 5/8 thread, no thread adapter, and wanted to keep as much length as possible.
Sorry if I made that confusing in my first reply.
Tbac thread chart below. Tried to highlight the 5/8 line. 0.725 min barrel diameter recommended.