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