(Get 5 kills in one Dead Eye burst while riding a moving train - just one of the objectives of the Legendary Marksman Social Club Challenge.)

Take a shot at being crowned a "Legendary Marksman" via the latest unlocked Red Dead Redemption Social Club Challenge (press pause and visit the Social Club tab in the pause menu if you need info about the Challenge).  

All three objectives of the Legendary Marksman Challenge must take place on a moving train instead of in a specified Gang Hideout.  It doesn't matter which train you hop on or where it's headed, as long as you've completed the prerequisite Sharpshooter Rank 4 Ambient Challenge and are equipped with a trusty sidearm and steady aim.

To be crowned a Legendary Marksman you must tackle these three objectives while in motion aboard a train:     

• Kill 20 animals and/or humans 
• Get 5 kills in one Dead Eye burst 
• Set 'Targeting mode' to expert for the entire ride 

 
(Taking down a bird counts for just as much as if you were to take down a bandit.  Shoot anything that moves.)

(It doesn't matter whether you ride on top of or inside the train, just get the job done.)

Play the Challenge and then visit the Social Club to check out where your time stacks up on the Rockstar Games Challenge Leaderboards.  All you need to take full advantage of any Social Club Challenges is a Social Club account which can be created in-game or on the web by going here and registering. 

If you earn at least a silver medal in this Challenge, you will unlock the Beastmaster cheat - great in situations where you want animals to become allies (do note that enabling a cheat will disable saving and the ability to earn Achievements/Trophies).  Get your Social Club membership and see if you have what it takes to rise to the Challenge.