The Gimli That Axe achievement seems to be asked about alot on the Killing Floor forums because of it not unlocking properly, so here are the details to get this to work for you achievement hunters.
After getting this Killing Floor achievement you’ll be able to purchase the powerful Dwarfs?! two-handed axe with knock back effect from the trader. There are a couple issues which make people think this is bugged, but really isn’t if you follow these steps.
First, make sure your Steam Profile is public so Killing Floor will be able to determine if you own and have unlocked the ‘Not-a-war-hammer’ achievement in Dwarfs?!. To do this, click on your Steam profile, click ‘Edit Profile’ then click the ‘My Privacy Settings’ tab.
If you purchased the video game Dwarfs?! you can already buy the Gimli axe from the trader, but to get the actual Gimli That Axe achievement you’ll need to get the ‘Not-a-war-hammer’ achievement in Dwarfs?!. To do this you need to get a cumulative total of 40k gold in the Arcade version of play. That should be straightforward.
If you don’t own Dwarfs?! you can still play Dwarfs?! F2P to get the ‘Not-a-war-hammer’ achievement from the free to play version.
Next time you load Killing Floor it should check your public Steam profile for this Dwarfs?! achievement, and if found, unlock the Gimli That Axe achievement.
Note if you have both Dwarfs?! and Dwarfs?! F2P in your Steam library, make sure the first game listed has the ‘Not-a-war-hammer’ achievement as the Killing Floor check seems to stop at the first Dwarfs?! entry. However the Dwarf?! achievements should transfer between the two games when they are each started, so you only have to unlock ‘Not-a-war-hammer’ once.