That gun is the M1919A1 .30 caliber. The early version of the ones you all seem to think of as the genaric .30 cal. The M1919A1 was water cooled and as such VERY heavy, as such it was mainly used as a vehicle mounted weapon. But it was used widely by the US infantry early in the war untill the aircooled M1919A3 (the one you allways see in games) entered wide-spread use about mid to late 1942.
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SS-Panzergrenadier