The first BM-59s started out as M1 rifle receivers, converted to 7.62 NATO and made selective fire. Later new receivers were made in Italy and several versions were made for the Italian army. Still later, some semi-auto versions were imported into the U.S. under the BM-62 model number, the change being necessitated by a BATF ruling that the BM-59 was, by definition, a machinegun.
The BM-59 was, in brief, the Italian version of the M14.
Jim