Good morning , I am Brazilian and my English is not so good .
At first I had a hard time getting this achievement and yesterday finally got .
I'll try to help you guys :
In Xbox One you just need to kill three enemies or more only 1 time. While the Xbox 360 you need to achieve 10 medals in three deaths or more .
At first I could kill 3 enemies with a weapon Storm specialist Phopet 3 times. And after some matches could kill 3 enemies 7 times to Scythe of the Reaper weapon. How to order 10 medals I thought I'd unlock the achievement. But it failed. So I tried 3 more medals with Scythe and it worked.
It is therefore necessary 10 medals with a single weapon. In other words, it is necessary to kill enemies 3 or more in a short time 10 times with the same expert gun. Remembering that it is cumulative, you can achieve in several matches.
Tip: Play more frequently Kill Confirmed and Domination. They are great game modes where you have enough players together. In Domination generally has 3 to 4 players in the 'A' or 'C'.
I adapted better with Scythe to have a cadence of quick shot. Gravity Spikes is also very useful when you have several next enemy, the weapon storm tera not always fortunate to have several next enemies, as if a shot had been enough as it reaches the next enemies.
Use as perks : Overclock , it is unlocked at level 20. It makes you able to enable faster specialty.
Also important to use the scorestreak : UAV to locate your enemies and be able to use the specialist weapon at the time to be more effective.
Good Luck !