Large Capacity Ammunition Feeding Device Act - Amends the Brady Handgun Violence Prevention Act to prohibit: (1) the transfer or possession of a large capacity ammunition feeding device, except for such a device lawfully possessed within the United States on or before the date of this Act's enactment; and (2) the importation or bringing into the United States of such a device.

Exempts: (1) the transfer or possession of such a device by a federal, state, or local agency or law enforcement officer; (2) certain transfers to licensees under the Atomic Energy Act of 1954; (3) possession of such a device transferred to an individual upon retirement from a law enforcement agency if such individual is not otherwise prohibited from receiving ammunition; and (4) the manufacture, transfer, or possession of such a device by a licensed manufacturer or importer for authorized testing or experimentation purposes.

Sets penalties for violations.

Requires a large capacity ammunition feeding device manufactured after this Act's enactment to be identified by a serial number that clearly shows that the device was manufactured after such enactment.