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.
Kill 25 enemies as they rappel using the Nagant sniper rifle. Unlocks the "Constable" mask, the "Silenced Barrel" and the "Long Barrel" for the Nagant sniper rifle, "Gunsmoke" material and "Dazzle" pattern.
Kill 10 enemies within 10 seconds using the Buzzsaw 42 light machine gun. Unlocks the "Old Blood and Guts" mask, "Light Barrel" for the Buzzsaw 42 light machine gun, "Patriot" material and "Captain War" pattern.
Equip a Broomstick pistol with the Damper.L 44 Nozzle and the Barrel Sight 44. Unlocks the "British Bulldog" mask, "High Capacity Mag" and "Holster Stock" for the Broomstick pistol, "Army Green" material and "Filthy Thirteen" pattern.
Kill 25 enemies while in stealth using the Trench knife. Unlocks the "Red Bear" mask, "Short Barrel", "Suppressed Barrel", "Short Mag", "Folded Stock", "No Stock", "Solid Stock", "Heatsinked Suppressed Barrel" for the Patchett L2A1 submachine gun," Barrel Sight 44", "Damper.L 44 Nozzle" for the Broomstick pistol, "Red Sun" material and "Death Dealer" pattern.