Sharpshooting Challenge - Hats Off and Disarm

There is a sharpshooter challenge that involves shooting the hat off an enemy, then disarming him within 3 seconds.

One solution would be to try doing this during a duel. Hit the hat then aim for the gun to disarm the enemy.

Another approach is to go into Mexico and shoot enemies with sombreros, as those hats are a lot easier to sight and hit.