The Gage Historical Pack Add-on for PAYDAY 2 has 5 achievements.
In the Hoxton Breakout job, complete the heist while you and your four man crew are wearing one different "Historical" mask each on the OVERKILL difficulty or above. Unlocks the "Discreet Stock" and "Short Barrel" for the Nagant sniper rifle, "Precision Barrel" for the Broomstick pistol, "Extended Mag" and "Long Barrel" for the Patchett L2A1 submachine gun and the "Heatsinked Suppressed Barrel" for the Buzzsaw 42 light machine gun.