Rex left the army after an unknown conflict went south and left him unable to use lethal force. Unfortunately, a lifetime* as a soldier makes for few job options. By working as a "battlefield custodian" he stays close to his core competencies but in more of a support capacity. Rex has configured his load-out to reflect his new goal of pacifism. He carries a shotgun with one blank round, one rock salt round, and then regular ammunition. In his kit, he keeps a variety of flash and stun grenades to further turn the tides in his favor. He still retains a carbine and hold out pistol with standard ammunition, although it's reserved for worse-case scenarios.
Vaughn, however, just wants to shoot as many rounds as possible at any takers.
*minus a small stint as a male model