The Gage Shotgun Pack Add-on for PAYDAY 2 has 12 achievements.
In the Rats job, complete the heist while you and your four man crew are wearing one different "Shotgun Pack" mask each on the OVERKILL difficulty or above.
Complete any single day of a heist, killing at least 50 enemies using only your melee weapon.
Hit 4 enemies simultaneously using any shotgun and HE rounds. Unlocks the "Solid Stock" for the M1014 shotgun.
Kill 10 snipers using any shotgun and flechette ammo. Unlocks the "Long Barrel" for the Raven shotgun, "Clint" mask, "Leaf" material and "Monkey Skull" pattern.
On the Nightclub job, kill 25 law enforcers using your shovel. Unlocks the "Short Barrel" for the Raven shotgun.
Kill 50 Shields using any shotgun and slug ammo. Unlocks the "Collapsed Stock" for the M1014 shotgun.
Complete any day of a heist in stealth with a Locomotive 12G shotgun modified with the "Silent Killer Suppressor" equipped. Unlocks the "Suppressed Barrel" for the Street Sweeper shotgun, "Rutger" mask, "Banana Peel" material and "Banana" pattern.
Complete any heist by killing at least 50 enemies and getting 101% accuracy or above using any shotgun. Unlocks the "Long Barrel" for the M1014 shotgun.
Kill 10 Bulldozers using any shotgun and 000 buckshot ammo. Unlocks the "Long Barrel" for the Street Sweeper shotgun, "Steven" mask, "Sparks" material and "Chief" pattern.
Beat a Shield to death using the Telescopic Baton.
Get 7 enemy headshot kills within 11 seconds using any shotgun. Unlocks the "Short Barrel" for the M1014 shotgun, "John" mask, "Explosive" material and "Terror" pattern.
Own the Locomotive, Street Sweeper, Reinfeld, Mosconi, Izhma, Raven and M1014 Shotguns. Unlocks the "Flip-up Sight" for the Raven shotgun.