The figures look great, but hardly heavy artillery, those rounds look rather anemic.

My first thoughts too. The rounds look like 122mm rounds, which was medium artillery for the Soviet Union in WWII. 122mm is now their light arty. Furthermore, the actual figures are carrying what looks like 75mm rounds, WWII-era light artillery.

Although the built up models show 76mm rounds , the box art shows 122 and 152 ammo boxes . The box art does say " new heads " so this is probably an older kit ( SU 76 crew ? ) given some new life .

They are from the SU-76 kit. New Ammo and and new heards. If you look closely at the sprues, you will see the tanks crew helmts.