These are statistics which determine the effectiveness of any gun. The stats alone do not make the gun; testing out a gun is imperative if you're choosing a main weapon. They hold a minimum value of 1 and a maximum value of 10.
A gun's attack is the raw damage. It is the average between the ground damage and the air damage and close-range to long-range damage, if they are different.
This is the average speed of the gun rounds. This usually varies inversely with Attack.
This is the ability of the gun round to continue to pursue the foe.
Reload refers to how quickly the gun can produce another shot.