I have gotten the chevo before. This was before I had a gamertag. Im stuck at 99.9% here is what I have done;
I have the LeMat revolver, Semi-Auto Shotgun, Buffalo Rifle, Carcano Rifle, Evans Repeater, and Mauser Pistol.
I have every house in the game, every outfit done, and every challenge done.
I have every bounty person marked as a ? with no name.
I also have all of the 19 Strangers tasks done.
All missions are done.
All gang hideouts completed.
All minigames are done.
All locations discovered.