Here is the full list of all 52 GUNGUNGUN achievements.
Get 500 kills with the Stechkin
Get 5000 total kills
Get 500 kills with the Rhino
Get 500 kills with the Shotgun
Get 500 kills with the Kalashnikov
Get 500 kills with the FAL
Get 500 kills with the USP9
Get 500 kills with the MP5
Get 200 kills with the Rhino
Get 200 kills with the Stechkin
Collect 20 hats
Get 200 kills with the USP9
Get 200 kills with the Martini-Henry
Get 500 kills with the Martini-Henry
Collect 10 hats
Get 200 kills with the Shotgun
Get 200 kills with the FAL
Get 200 kills with the Kalashnikov
Get 1000 total kills
Get 20 kills with the Martini-Henry
Kill five heavies with the Martini Henry
Save up 10,000 in the bank
Get 200 kills with the MP5
Survive for more than 5 minutes in a single round
Score 1,000,000 points in a single round
Score 500,000 points in a single round
Survive for more than 3 minutes in a single round
Stand still for 30 seconds straight
Collect your first hat
Earn your first 1000 total bounty
Save up 2000 in the bank
Get 200 total kills
Get 20 kills with the USP9
Get 20 kills with the FAL
Get your first 30x combo
Score 50,000 points in a single round
Get 20 kills with the MP5
Get 20 kills with the Stechkin
Get 20 kills with the Kalashnikov
Cause 5 enemies to die by way of explosion
Get hit by a heavy
Get 20 kills with the Rhino
Get 20 kills with the Shotgun
Get your first 10x combo
Survive for more than 1 minute in a single round
Earn 1 Million in total bounty
Collect 28 hats
Kill 3 bandits with a single Martini-Henry shot
Heal 5 times in a single round
Pick up one of each weapon in a single round