When you approach the weaponsmith in the football stadium, turn around and see a shooting range through a door. Enter and beat
high score to gain the trophy.
Make it easier, turn on aim assisst (I found during these chapters it turna itself on, I'm not sure if this is a glitch or not).
You need over 83points to gain the bronze trophy. Although, even without aim assist it's very easy, the target stays static, so you just need to keep aiming at the red target until fully focused. 9 shots at 10points each. Quickest sharpshooter challenge in gaming history.