I have been doing a bit more research on the subject and found this on the minigun installation.
". . .The location of the side-firing gun in relation to the center of gravity made both aircraft tail heavy. In the Peacemaker the condition proved so dangerous that forty pounds of lead had to be inserted under the engine cowling to restore some semblance of equilibrium. To overcome the lack of balance required a heavy hand on the controls and forced the small-framed South Vietnamese to wrestle the control stick with both hands in performing basic maneuvers. As if this were not enough, neither range nor payload lived up to expectation; a minigun ship carrying one thousand pounds and flying a distance of one hundred nautical miles could remain on station just thirty minutes before turning back to refuel.
The XM197 Armament System evaluated in this test is similar to the M61 Vulcan 20mm rapid fire cannon. The XM197 consists of three rotating barrels instead of six and has a rate of fire of approximately 400 rounds per minute (rdpm) slow rate, and 700 rdpm fast rate. For the test reported here, the gun was pedestal mounted just behind the pilot's seat in the Fairchild-Hiller Peacemaker Aircraft. The M61 and XM197 20mm guns are automatic aircraft cannons for use against aircraft and ground or seaborne targets. These guns are electrically or hydraulically powered, belt fed or linkless fed, and electrically fired. A round of ammunition is fired through one barrel at a time, as the barrels and rotor assembly rotate once around the rotor housing. . ." (edit note: from "AC Gunships")
