sentences: (This date needs to be confirmed since known M2 survivors have serial numbers indicating that at least 90,530 M2's had been built by 1953).Some sources state that many M1's were reworked to M2 standard by fitting hood over foresight, changing the rear sight and fitting a stronger spring to the ejection port cover and that when this upgrade was done the M1 designation was overstamped M2, but examples of M1's that have been upgraded to the M2 exist where the original M1 stamp has not been over stamped.