Three-dimensional source characterization is crucial for determining noise metrics produced by operating a firearm in indoor environments. Anechoic measurements for sound power and directivity measurement are challenging for small caliber firearms. In order to create high fidelity source models of an M4A1 firearm (firing blanks), a team from Ball Aerospace, Inc., the Air Force Research Laboratory, and Brigham Young University conducted an expansive characterization within an anechoic facility located at the Owens Corning Acoustic Research Complex using a two-meter spherical microphone array centered on the muzzle of the weapon. The array consisted of a quarter sphere of over forty microphones at various elevation and azimuth angles. By rotating the weapon, an entire closed sphere of over one hundred points were sampled with multiple shots. Differences in directivity, sound power level and shot to shot repeatability are examined for two weapon configurations. These differences reinforce the idea that accurate source characterizations are required for modelling small caliber firearm noise propagation. The views expressed are those of the author and do not necessarily reflect the official policy or position of the Department of the Air Force, the Department of Defense, or the U.S. government.