Aliens Colonial Marines
60 Achievements
1,250
35-40h
Field Modified, Kill Certified
Upgrade every slot for a weapon
20
How to unlock the Field Modified, Kill Certified achievement in Aliens Colonial Marines - Definitive Guide
I got it with the pump shotgun, changing the defaults to flèchette rounds, custom port, laser targeting, Midas touch and expanding shot.
When I changed the last item the acheievement unlocked.
Armat A7 Sound Suppressor
Armat Laser Targeting System
A27 High Velocity Rounds
Note: You may also need to change the weapon skin to something other than the default skin.
EDIT: After doing some checking, it seems that all of the pistol upgrades are related to leveling up and/or completing missions. Completing challenges is not necessary for this one. Also, it seems that the weapon skins do not affect this achievement, and you can unlock the achievement regardless of weapon skin.
If you do this with the Service Pistol, you will also unlock this achievement:
For this achievement, weapon skins DO count! While the pistols are still the fastest for the achievement, you must have some challenges completed to have at least one of the pistol skins. (I had the gold skin for service pistol.) For more info, see "I Can Handle Myself."
Each weapon (with the exception of Pistols) is divided into five sections – Alternate Fire, Attachment, Sight, Skin and Fire Mode. To earn this trophy, you simply need to purchase at least one upgrade in each of these slots. To upgrade a weapon, select the "Arsenal Upgrades" option either on the Main Menu or the Pause Menu of the campaign and choose the weapon that you wish to upgrade. It doesn't matter which upgrade you choose in each slot – you only need to buy it.