Up your arsenal 3

[Bugsy]

Greetings assassins,

So for this challenge of "Birdie's Gift" you are supposed to win the competition with sniper rifle, right ? I completed the challenges "Up your arsenal 1 & 2" but number 3 still has a lockpad... I absolutely don't know why. I already used all weapons to win the contest, and especially the sniper rifle, but nothing seems to work right now. Would you guys have any idea about what I could do to finally complete this challenge ?