So as mentioned, this achievement can be a little glitchy with recognizing you as the top player. But putting that aside, here is a good set up to have for a match of Blast in order to be top,
- Scan Pulse
- Jet Pack (Not hugely important but helps).
- Scout Trait Card
- Either Blast Pistol (SE-14C is what I use) or the Shock Blaster (CA-87)
Pick a map where you can surprise enemies such as Imperial Station or Hanger.
Now the very simple idea with this set up, is that you can use your scan pulse frequently to get the jump on enemies (especially around corners), Both weapons are quick fire or quick kill which helps, as does the impact grenade (as you can throw it before they even come around the corner to see you).
Finally, the biggest strength of this set up is the Scout Trait, this will allow you to run around the map undetected on the radar, thus enemies have less chance of knowing you are around the corner.
More and more people have confirmed that it unlocked upon the timer running out, Try to persist with matches in this manner, getting games that have fewer people should help.
Hope this set up helps