His compiled service records are filed under the surname McCreary as are most company muster rolls, however, many other cards show McCrary. Officially, then, it is McCreary, however, if you wanted to search further, I'd start with the 1860 census.
To further complicate matters, he signs a pay voucher on October 4, 1862 with "his mark," an 'X' under the name B. McCray. Witnessed, most likely by an officer in his company.
What do they Soldier's Home records show?
George Martin