The rifle Hardie carries on the trip is a lever action rifle, the ammo is stored in the tube below the barrel, nose to primer of the cartridge. This doesn't fit the ammo in the bandolier that he is wearing. If that ammo were used in the rifle he was carrying, the first shot would cause the bullet to strike the primer of the cartridge in front of it, causing a chain reaction up the tube of all the cartridges.