Hope someone knows military history could answer this question. Today in Russian military they are still using 122mm and 152mm caliber gun. I know these numbers came from Imperial Russian period and may related with smooth bore gun. How the Russian artilery weapons transit from smoothbore period to modern period?
I answered a similar question here. The 122 mm and 152 mm calibers (as well as many others) originate from European rifled calibers, not Russian smoothbore guns.