When I was holding a .44 Magnus, with 6 bullets in the gun, and 5 extra, I put the ammo into a storage container. All 11 bullets went into the container, but I still had 6 bullets in the gun. (Only tried with .44 Magnus and .44 Hollowpoint ammo)
Steps to reproduce:
1-Hold a .44 Magnus in your hand.
2-Load the weapon.
3-Open a storage container and put in the ammo.
4-All of the bullets you had should be in the container, and you should still have 6 bullets in the gun.