Specifically the late 16th-early 17th century. Apparently certain sizes were common enough that writers would refer to "full musket bore", "bastard musket bore", or "caliver bore" but don't seem to make clear what exactly these sizes were. Can anyone clarify what was most common among different nations? Sources would be appreciated.

Look up contemporary military manuals like Hexham, Barriffe, or Cruso. They usually mention their preferred calibres for firearms. If you don't have the time or can't be bothered to do that, this older thread might have some useful information.

https://myArmoury.com/talk/viewtopic.php?t=13211