A simple calculation about guns barrels lenght.
125 x 52 = 6,500
125 x 50 = 6,250
125 x 48 = 6,000
120 x 55 = 6,600
120 x 52 = 6,240
120 x 50 = 6,000
120 x 48 = 5,760
120 x 44 = 5,280
Rh-120/L55 is still longer than any 125mm gun of the 2A46 family and their clones with all possible gun...