Here is the full list of all 30 Endless Firepower achievements.
Kill 100 enemies in 1 run
Kill 500 enemies in 1 run
Kill 1,000 enemies in 1 run
Kill 5,000 enmies in 1 run
Collect 100 guns
Collect 500 guns
Collect 1,000 guns
Collect 5,000 guns
Collect 10,000 guns
Collect 1,000 gears in 1 run
Collect 5,000 gears in 1 run
Collect 10,000 gears in 1 run
Collect 50,000 gears in 1 run
Reach level 5 as recruit
Reach level 10 as recruit
Reach level 20 as recruit
Reach level 50 as recruit
Reach level 100 as recruit
Reach level 5 as soldier
Reach level 10 as soldier
Reach level 20 as soldier
Reach level 50 as soldier
Reach level 100 as soldier
Reach level 5 as engineer
Reach level 10 as engineer
Reach level 20 as engineer
Reach level 50 as engineer
Reach level 100 as engineer
Unlock Soldier
Unlock Engineer