Here is the full list of all 26 Call of Juarez: Gunslinger achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Find and kill Johnny Ringo.
Give it to them straight about your meeting with Pat Garrett.
Unlock a skill.
Forgive your lifetime nemesis.
Kill your lifetime nemesis honorably in a duel.
Collect all Nuggets of Truth.
Complete all Arcade missions.
Score the maximum of 3 stars in any Arcade mission.
Get all Arcade Mode stars.
Unlock all skills in Story Mode.
Unlock both exclusive weapons in a single category of skills in Story Mode.
Kill a bird during a winning duel.
Fight in Concentration for 15 minutes.
Shoot a flying stick of dynamite and the one who threw it on a single Concentration.
Shoot through a hole to kill an enemy that hides behind a shield.
Reach combo level of 20.
Complete the Story on hard difficulty.
Find all Nuggets of Truth in a single mission.
Discover a shipwreck in the Missouri swamps.
Find and kill Jim Reed.
Complete the Story on any difficulty.
Complete the Story on True West difficulty.
Complete the duel challenge, winning all duels honorably.
Kill a shotgunner with a close-range shotgun blast.
Win a duel honorably in under 0.6s.
Kill 5 enemies when falling down through the air.