Thank you! I can make the hammer valve combined with the quick exhaust valve, I'm just not sure if it is worth it. Would it boost performance or nah?

Hello, people of Spudfiles! This is my first bolt-action airgun, and I've no idea what pressure it requires. The rifle will hopefully shoot a 0.357 caliber slug out to 300 yards out of a 21-inch barrel, powered by a paintball hpa tank. I'm hoping to get maybe 600-900 fps. If I could get calculations...