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