Completion bonuses:
Successfully complete story mode to unlock Magruder's seven barrel Nock gun.Successfully complete story mode and all side missions (100% completion) to unlock Reed's armored horse and Magruder's Cannon Nock gun. .69 Ferguson Rifle:
Defeat Hollister. Apache Shirt:
Successfully complete the Hunting missions. Cavalry Sword:
Defeat Reed. Dual Peacemakers:
Defeat Reed. Silver Spurs:
Successfully complete the Pony Express missions. Unlimited ammunition:
Take a barrel of TNT from the Badlands mine. Find the abandoned house in the Badlands where the buffalo graze. Go to the back of the house on the outside. Face the chimney (looking west) and place the TNT barrel on the left side of the chimney. Blow up the TNT barrel to open a hole in the ground with unlimited ammunition for all weapons. Glitch:
Here's a fun glitch my sister found while messing around. First save your game, then go to the ferry on the apache side(make sure you have a horse)go to the right side(away from the ferry)where the river and a cliff meet to form a corner. Now turn to the cliff and walk into it then hit A to rear up this should send you floating up into the air. PS this may take several tries but it does work, I've done it many times to make sure. Also you can do the same thing but jump with various results. Infinite Whiskey:
For infinite whiskey look in the chicken coop in Hecht ranch by the windmill. | 
Gun - Game Cube
