You should give an indication of how high up this ship of his is. If it flies at the height that airplanes usually do, which is roughly five to eight miles, and the gun being fired from it has the muzzle velocity of a powerful modern sniper rifle, you're looking at a delay of 7 to 12 seconds between firing the gun and the bullet reaching ground level. Which, obviously, would make it very hard to hit anything.
In fact, that number is when ignoring air friction. If we're gonna get technical, there's no way that gravity will accelerate a bullet beyond the muzzle velocity of a sniper rifle. The muzzle velocity of a powerful sniper rifle is mach 3, or 3400 feet per second, whereas the terminal velocity of a falling bullet is some 300 feet per second. An exceptionally aerodynamic bullet might go faster, but not to that extent.
Now, i don't mind using artistic license on gun physics, but you'll have to state it when you do, such as by saying "the bullet only has one second of travel time". Otherwise misunderstandings will happen. Alternatively, if you wanna stay scientifically accurate, you could say the bullet has a propulsion source, like a tiny rocket, to counteract friction. And of course lower the altitude of the ship. At 1 mile the travel time would be 1.5 seconds, provided your bullet moves at normal sniper rifle speed.
Edit: More importantly, none of those driods are what tier you say they are. With durability like steel, superhuman strength (for the first two) or speed (for the third), good combat skills and powerful technology, they should easily be tier 4.