The T3 was originally developed to be a carbine sniper rifle. Since the range and accuracy of the carbine leave a lot to be desired, it never got to the field. However at the same time the military was developing infrared technology and someone figured out that with the limited range of the infrared and the heavy weight of the units, the carbine was the perfect firearm for mounting the unit. The original T3 had the scope mount built diectly on the receiver. It was not removable as it is on the M3 It was brazed right on to the receiver and became integral with it. The M3 has a removable mounting bar that attaches to the barrel and the dovetail. As to the flat bottom stock configuation, this is an early T3/M3 feature. The early versions of the infrared units had the "lamp" mounted on the underside of the stock while the scope was mounted on top. The flat bottom was where the lamp was mounted. The later units had the lamp mounted on to of the scope. The reason for the change was because with the lamp mounted on the bottom, the operator often had to stand to use the unit so that the lamp was clear of the bush and grass. With the lamp mounted on top, the operator could stay down and under cover much better, avoiding random counter-fire.