In 1940 there were two versions of the 172 grain Ball cartridge, the M1 and the M1 Alternative (M1B1). The alternative had a bullet with less antimony in the core but both used gilding metal jackets.
Like the M1, the M2 was also made in an alternative version having less antimony in the core. But in late 1942 a bullet with a clad steel jacket was authorized and the cartridge was called the Ball, Cal .30 M2 (Alternate). By the fall of 1943 the copper shortage had eased and the GM jacketed bullets were once again authorized. The last lot with the GMCS bullet was accepted in February, 1944.
It seems odd that the same designation would have been used for two different cartridges. Maybe there’s a clue in the use of the words Alternative and (Alternate)? The boxes I have are are marked Alternative and have the GM jacketed bullet. I have not seen a box marked Alternate. Does anyone have such a box and can tell us what cartridges are inside?
Notice that the M1 tracer with the GMCS bullet is also called (Alternate).