Full list of all 20 Gun Bros achievements worth 200 gamerscore. It takes around 30-35 hours to unlock all of the achievements on Windows Phone.
Reached level 100
Completed Revolution 10 on any planet
Serviced 50,000 targets
Completed 100 unique perfect waves
Purchased 60 power ups from the store
Reached level 50
Saved 100,000 coin
Serviced 1000 targets with pistols
Serviced 1000 targets with rifles
Serviced 20,000 targets
Serviced 1000 targets with shotguns
Completed Revolution 1 on any planet
Serviced 1000 targets with spread guns
Purchased 8 guns from the store
Serviced 5,000 targets
Reached level 20
Purchased 20 armor pieces from the store
Destroyed 30 Zombies in a single Streak
Completed a Bro-Op Challenge!
Got a Bro Buff