Because if the gun is mounted on the centerline of the aircraft, it's more natural for the pilot to aim. Also, you can fire out to the full range of the ammuni

Because if the gun is mounted on the centerline of the aircraft, it's more natural for the pilot to aim. Also, you can fire out to the full range of the ammunition. Guns mounted on the wings had to be canted inward so that their pattern of fire intersects at some distance in front of the aircraft, so you only get the full firepower of all your guns at or around that specific range. https://en.wikipedia.org/wiki/Gun_harmonisation https://en.wikipedia.org/wiki/Gun_harmonisation