Odd period question regarding .50 caliber

I quite expect this is part of Apple’s text system, but perhaps someone knows a fix?

Typing a paragraph in Scriv, a sentence includes the term “.50 caliber”. On a line wrap, the “.” ends the line and the “50” goes on to become the start of the next line. Not a bit deal, but every time I work through the paragraph…

This is indeed part of the text system. However, you can add an invisible character before the period to force it to break the way you want. Go to Edit > Special Characters, in the panel that appears search for “Word Joiner” and enter that character before the period. In the next update I’ve added an Edit > Insert > Word Joiner menu item to make this easier.
Hope that helps.
All the best,
Keith