Quote Originally Posted by Ken White View Post
(...)the 152mm Howitzer versus the Czech and German 150mm. The 120mm Gun though was purely a function of trying to equal the capability of the German 105mm.
Their 152 mm gun-howitzers were actually superior to German WW2 heavy howitzers. The small difference in calibre was more about metric vs other measurement system and history than anything else. Many official "150" mm howitzers of the era were in fact 149.1 mm pieces.

The only 120 mm guns used by Russians were IIRC WWI vintage guns. The calibre was a popular calibre pre-WWI and the Russians imported the design.
Their 122 mm gun has a similarly old history, being a traditional calibre and not really related to a competition with 105 mm.
122 mm is actually a superior calibre in comparison to 105 mm if you don't need light weight. 149-155 mm is relatively if you desire smoke or frag effect, yet 122 mm is much better than 105 mm for ICM and blast effect and achieves good range more easily than 105 mm (less V0, less barrel wear).

As of today I'd prefer a new 122 mm SPG over a 155 mm SPG because range isn't that important and most countries banned DPICM.