Here is the full list of all 42 Gunscape achievements.
Publish your first map
Kill 500 players with the Gauss Rifle
Kill 1,000 players
Kill 500 players with the Dual Zhotguns
Won 25 Survival games
Kill 100 players with the Flamethrower
Killed yourself 50 times
Win 25 Infection games
Win 25 CTF games
Play your first Infection game
Kill 100 players with the ID Disc
Return 25 flags in CTF
Kill 50 players with your Fists
Kill 50 players with the Speargun tripwire
Win 50 Deathmatch games
Steal 25 flags in CTF
Place a flag in your map
Place a Checkpoint in your map
Play your first Team Capture-The-Flag game
Kill 5 players with a knife
Use the Freezethrower to slide 3 blocks
Play your first Team DeathMatch game
Play your first Free-For-All DeathMatch game
Rate another player's map as bad
Play your first Gun Game game
Kill an enemy player
Rate another player's map as good
Finish the Blowfish campaign
Kill a dinosaur boss
Kill 100 AI enemies
Kill a robot boss
Finish the first Blowfish campaign map
Create your first map
Place 100 blocks in Build mode
Place your first block in Build mode
Play your first split-screen game
Place 10,000 blocks in Build mode
Build a multi-map campaign map
Kill 1,000 players with the PFG
Kill 1000 players with the E-Bow
Program 5 Terminals
Kill 5,000 AI enemies