120mm is the diameter of the round, and hence also roughly the
internal diameter of the Gun barrel. 120mm/L44 means the length of
the barrel is 44 times of 120mm = 5280mm.
The 120mm/L55 has a barrel length of 55 X 120mm = 6600mm.
The longer the barrel, the longer the range, because it allows for
a longer duration of acceleration in the gun (i.e. force is applied
on the projectile for a longer duration).
