It’s early in the afternoon when the deputy steps inside a 55-foot-long tractor-trailer that’s been reinforced with ballistic steel panel walls and a granular rubber bullet trap. With eyes and ears protected, she takes aim inside the Orange County Sheriff’s Department Mobile Pistol Range (MPR). The trailer, parked behind the OCSD’s South Operations substation in Aliso Viejo, is equipped to absorb blasts from a variety of handguns and shotguns. From the outside, the shots are merely muffled pops. Inside, they’re painfully loud. Deputy Inv. Maria Bowman, who handles general crimes for the City of San Clemente, spends a lot of…