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