>>314755218don't listen to this fuckign nigger.
MA5B was the service rifle prior to halo 2, 60 rounds of 7.62mm FMJ. BR55 entered service around halo 2 and replaced the older MA5Bs. Then circa Halo 3, the MA5C was introduced, which had a smaller magazine, due to "spring strength" issues of the MA5B's 60 round magazine.
The MA37 is the one in reach, and is kind of a canon-mind fuck because canononically it should be the MA5b but i guess the UNSC army compared to the marines had a different varaint of MA5.