Impractical. The effective ceiling of an MQ1 Predator is 25,000 feet, which approximates to 4.5 miles.
The effective range of a Barrett M82 (50 Caliber rifle) is approximately 6,000 feet, and that's not shooting straight up.
Point blank (which, despite the common vernacular meaning 'really close', actually means 'the range of the bullet before you have to adjust for elevation') is 1500 feet, past that, gravity begins taking over.
TL;DR, the range of a Predator drone is definitely greater than the naked eye's visibility range, and even with optics, target acquisition is nearly impossible, and even if it weren't, unless it's flying very low relative to its ceiling, you can't hit it anyway.