If anyone cares, there will probably be a .357 Mag revolver/lever rifle included as a weapon in BF3. I'm basing this off of the .357 casings I saw in the EA Pwned video.
Oh, and I think there might be ammunition sharing, as in the PS3 demo on Fallon, the HUD indicated the current weapon's caliber (5.56x45mm, since it was a M4.) So we could see common-caliber ammo pools. For example, you might intentionally choose to carry a MP5 and a M9, because then all of your weapons use 9mm Para.