E bravo Fausto.

The headstamp is not LN but LM. They used a bad bunter for the headstamp.
LM stands for Lowell Ordnance Plant in Lowell, Mass. This plant was under control
of Remington Arms Co. and produced Cal. 50 ammunition from Nov. 1942 till Dec. 1943.
In total they produced about 71,5 million cartridges.

Ciao
René

grazie mille Rene'...