Groove diameter?

[Kivaari]

Has anyone slugged their Savage pistol bore?
Brower book suggests ".318 interior bore diameter".
That's a little vague not saying "groove diameter"
If this is so, wow,...why so big?

[Robinhood]

free bore diameter?

[Kivaari]

That's a thought...free bore or perhaps throat diameter....
CIP chamber has a .315 throat so maybe .318 SAAMI throat