Real easy on the level Birdie’s gift. You don’t even need to use the firing range to get it.
As soon as you start, head to the back right corner of the store where the 2 cops are and a mini shooting range. In the back of that room there is a vent you can crawl into and exit into an office. Wait there until the shop owner enters the office and stops by his desk. Take him out and grab the notebook that falls from him. Behind you is a safe. That notebook you just picked up is the combination for that safe. Interact with it and pick up the key inside. That key is for the silverballer case. Go back through the vent and exit to where the 2 cops are.
From here turn left and head straight to the front of the store. You will see a pillar and a fuse box. Interact with it. This causes the guy from behind the counter to walk away and inspect it. At this point walk around the cases and when the employee is away grab your silverballers. Cut scene happens then you can turn around and exit the level.