F = M x a
Since F does not change, . . .
Ouch!
Unlike the movies - where they are firing blanks - the M2 HB is most effectively fired from the tripod, using the Traverse and Elevating mechanism and both feet planted on the rear legs of the tripod.
Dang thing will kill effectively a lot further than you can see and it used to scare the crap out of the Germans in WWII since it ate their light armor up like nothing else.