Complex sentence: The Paris Gun was the largest gun built at the time, but it was surpassed by the Schwerer Gustav of World War 2, this fired shells up to 70 times heavier, but with only around half the muzzle velocity and less than one third the range.
Split into simpler sentences: The Paris Gun was the largest gun built at the time, but it was surpassed by the Schwerer Gustav of World War 2. This fired shells up to 70 times heavier, but with only around half the muzzle velocity and less than one third the range.