Full list of all 14 Small Arms achievements worth 235 gamerscore. It takes around 4-5 hours to unlock all of the achievements in the base game on Xbox 360.
The base game contains 12 achievements worth 200 Gamerscore, and there is 1 DLC pack containing 2 achievements worth 35 Gamerscore.
Awarded for playing someone online who has this Achievement
Complete the Single Player training mode with any character
Kill 2 opponents in rapid succession
Kill 5 opponents in rapid succession
Defeat 15 opponents in Challenge Mode
Defeat 50 opponents in Challenge Mode
Win 10 matches in Single Player or by playing on Xbox Live
Win 50 matches in Single Player or by playing on Xbox Live
Win 100 matches in Mission Mode or Battle Mode
Awarded for completing Mission Mode
Play 100 matches either offline or on Xbox LIVE
Score over 10,000 in the 'Shooting Range'
Complete Mission Mode playing as Ivar or Gullarp
Host an online match using the Iceberg or Village level