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.
Score the maximum of 3 stars in any Arcade mission.
Kill a bird during a winning duel.
Complete the duel challenge, winning all duels honorably.
Unlock all skills in Story Mode.
Win a duel honorably in under 0.6s.
Complete the Story on hard difficulty.
Complete the Story on True West difficulty.
Forgive your lifetime nemesis.
Collect all Nuggets of Truth.
Fight in Concentration for 15 minutes.
Complete the Story on any difficulty.
Kill your lifetime nemesis honorably in a duel.
Find and kill Jim Reed.
Discover a shipwreck in the Missouri swamps.
Kill a shotgunner with a close-range shotgun blast.
Unlock both exclusive weapons in a single category of skills in Story Mode.
Reach combo level of 20.
Shoot a flying stick of dynamite and the one who threw it on a single Concentration.
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.
Get all Arcade Mode stars.