Jack O'Connor's "Shotgun Book" (1965) gives 16ga bore diameters from the following manufacturers:
Winchester: .664
Browning: .665
Remington: .673.

I'd note that the same book shows a difference of .008 between standard 20ga bore diameters, and .005 between standard 12ga BD's.

Brophy's L.C. Smith book (with factory drawings) shows both Miller's .650 figure for the 16 as well as .652. Either case, a long ways from Remington's .673!.