:::::First, it didn't jam frequently.  Second, the rate of fire and muzzle velocity were comperable to other aircraft-mounted autocannon of the time.  Third, it was designed for use against bombers and tanks.  You can't say that it has less rate of fire than machineguns and that made it ineffective, it was a CANNON.  You can't say it was ineffective against fast-moving targets when it wasn't designed to be.  Find a reference to support your side.