Wait a second. While it would be hard to make the flight of a bullet curve in a horizontal plane is a controlled manner, it would be possible to make it curve.
If you move the gun to one side horizontally while firing, and keep the gun moving while the bullet is in the barrel, then the path of the bullet will curve, right.
The bullet will be moving in three directions (relative to the shooter). It will be moving along the axis of the bullet, it will be rising and then dropping (due to gravity), but that whole arc will be sweeping in the direction of the horizontal movement of the barrel.
So looked at from a bird's eye view, the bullet will in fact curve in a horizontal plane. I think that's the case - though I am not all that sure of the shape of the curve. But I think it would be possible by moving the gun to have the bullet strike a target to the right (or left of where the gun is pointing at the instant where the bullet leaves the barrel.
The problem isn't the curve, right?
The problem is getting the bullet to move to the right (or left quickly enough). Suppose the bullet has to move to the the right six feet. How much time does it have to do that?
Suppose the target is 100 ft away, and the bullet is traveling 1000 ft/sec when it leaves the muzzle. The bullet will reach the target in 1/10 sec.
If the bullet also has to travel 6 feet to the right in 1/10 second, that means that it need to move to the right at an average speed of 60 ft/second.
Mike