My friends and I have play all of those several and over and over to unlock weapon attachment but none of us have get any.
Do you have to be a specific level or what?
Can some one explain plz?

You can only unlock weapon attachments by YOURSELF in Brink, my brother was having the same trouble
He'd play with his friend and didn't understand why he didn't unlock the attachments, then, he played by himself and got the attachments
Hope this helps you :biggrin:

ok thx for answer, will try that l8r on, have only played with buddies =)

No problem man, anything to help out another person on Brink :wink_smile:

Yeah, you need to play them by yourself. That makes absolutely no sense. I hope Splash Damage changes that rule in an update.

Two more tips:

1. Only 1 star and 2 star challenges give attachments. The much harder 3 star challenges are purely for leaderboard scores.

2. If you're having trouble beating 1 star and 2 star challenges to get attachments, you'll have a much easier time if you're closer to level 1, because the enemy bots will be around your rank and level. If you need to lower your levels, sell your abilities to lower your level by 1, then buy one ability, then sell it, and repeat that over and over until you get to the level you want to be at.