When you are shooting from a moving target to another moving target, the situation gets even worse for slower, lighter, quicker decelerating bullets.
Suppose both aircraft are going 300MPH and the shooter is at a dead 6 position 900 yards behind the target (The ballistics computer wouldn't calculate the 131 round beyond 1525 yards... read on). {Each velocity will be increased by 440 FPS.} [300 MPH = 440 FPS = 146.66 YPS]
At 3.918 seconds, the 131 round has traveled 1474.6 yards. It had to go this far because in 3.918 sec. x 146.66 yds. = 574.6 yards that the enemy AC travels during bullet flight time.
574.6 yards (the AC moved) + 900 yards (originally from the target) = 1474.6 yards.
At this point it has a velocity of 702.9 fps.
But, the AC is going 440 fps, so the impact speed is only 258 fps (176 mph).
At 258 fps, its energy is only 13.6 ft./lbs.
The 50 Cal., on the other hand, only has to fly 1094 yards. It does this in 1.324 seconds.
1.324 sec. x 146.66 yds. = 194.2 yards that the enemy AC travels during bullet flight time.
194.2 yards (the AC moved) + 900 yards (originally from the target) = 1094.2 yards.
At this point it has a velocity of 1884.9 fps.
But, the AC is also going 440 fps, so the impact speed is 1444.9 fps (985 mph).
At 1444.9 fps, its energy is still a whopping 3277 ft./lbs.
So, the Mg 131 travels 1474 yards in 3.9 sec. and has 13.6 ft./lbs. of E.
The 50, however, has traveled 1094 yards in 1.3 sec. and has 3277 ft./lbs. of E.
eskimo