A firearm buffer includes a buffer casing having a casing chamber with open and closed ends, and buffer weight within the casing chamber. A buffer plug is received in the open end of the buffer casing. A cross pin extends through at least a portion of the buffer plug retaining the buffer plug on the buffer casing. A locking pin is longitudinally displaceable between a first position and a second position. In the first position, the locking pin is engaged with the cross pin and retains the cross pin in position with respect to the buffer plug. In the second position, the locking pin is disengaged from the cross pin such that the cross pin is removable from engagement with the buffer plug thereby permitting disassembly of the firearm buffer. A method of assembling a firearm buffer is also included.