Grand Theft Auto: San Andreas/Ammu-Nation

Requirements

 * Location: Any "large" Ammu-Nation that has a firing range, such as
 * Downtown Los Santos (The one with the huge gun)
 * El Quebrados

Go into the store and you should see a red marker in front of the salesman. If there is a second red marker, that is the shooting range.

Walkthrough
For each of four weapons you have to complete three levels, giving twelve levels in all. You have to complete all twelve levels consecutively to complete the challenge.

In each level you shoot at anthropomorphic paper targets. You have two competitors, and you have to finish the level before they do to advance.
 * Level 1: The targets are stationary, but each target is further back.
 * Level 2: The targets start far away and move closer.
 * Level 3: In this level you shoot at the same targets as your competitors. The targets descend from the ceiling on the left or right and follow a U pattern to the front, to the other side, then to the back.  You need to hit 20 targets before either of your competitors do.

The first time you attempt the challenge there will be a series of cutscenes which will explain this in detail.

Each time you complete the three levels you move on to a new weapon. The weapons are:
 * 9mm
 * Micro SMG: This can be easier because of the rapid fire. But there is a delay for reloading, so don't spray ammo unnecessarily.
 * Shotgun: The wide spray of the shot makes hitting targets easier with the shotgun. You can sometimes even take out two targets at once.  But it's easier for your competitors, too, making the third shotgun level one of the toughest challenges in the game.
 * AK-47: Requires much more accuracy than the shotgun.

Tips
Practice, practice, practice!

Rewards
The indirect reward is practice on the four weapons in the challenge, boosting your weapons stats, perhaps all the way to hitman. Completing all twelve levels consecutively earns progress towards 100% completion.