Here is a guide on how to access the Stone Hatchet and Double-Action revolver items for Red Dead Redemption 2 after completing the challenges in Grand Theft Auto Online.
Players who have completed the Double-Action Revolver Challenge in Grand Theft Auto Online will receive the Double-Action Revolver in Red Dead Redemption 2 as a part of normal Single Player story progression.
Players who have completed the Stone Hatchet Challenges in Grand Theft Auto Online will be able to discover the Stone Hatchet in the Single Player game. The Stone Hatchet is hidden in game and the location must be discovered by the player.
Although, we can just tell you the location right now, thanks to True Swoldier.
You can find the Stone Hatchet by visiting this location on the map - at a Native Burial site north east of Strawberry.
You will then see a formation of rocks which hold the Stone Hatchet in the center.