I was just reading about the recoil effect of the gun on the front.
At 4200 rounds/minute, 70 rounds are fired each second. A 0.425 kg projectile is accelerated to 1067 m/s every one seventieth of a second. This gives a recoil force of approximately 30 kN based on the relation above. On the GAU-8/A product homepage the recoil force is stated as 10,000 pounds-force, or about 45 kN, probably due to additional recoil from exhaust gas from the muzzle. The maximum combined output of the A-10 engines is 80 kN. Hence the recoil force of the gun is slightly more than half of the total thrust of the engines. While this is quite significant, it is not sufficient to stop the aircraft but it can noticeably slow the aircraft. In fact during test firing of the gun in the A-10 in the early 90’s the USAF experimented with putting a muzzle brake on the end of the gun and extending the nose of the plane out around this muzzle brake to vent the gun gases backwards. It was decided during this testing that the effect of the gun was not significant enough to warrant the added expense and complexity of adding this to every plane in the inventory.
The recoil of the gun is also evident in the mounting position of the gun. The gun is mounted off the centerline of the plane as the bullets leave the gun when the barrels reach roughly the 9 O’clock position when looking at the nose of the plane, thus the recoil forces of the gun are directed down the centerline of the plane. This was done because it was discovered during development of the platform that having the gun mounted on the centerline and thus the recoil forces off the centerline was enough to push the plane off target when firing the gun.