I don't know why, but distance between 400 and 200 last night it took 1000 rounds to effectively rip a wing off an opponents 110. And I mean, 1000 rounds on target!
Remember that the .303 is your basic deer rifle cartridge, ballistics aren't even quite as good as the .30/06. At 200 yards your velocity is significantly worse than a .30/30's muzzle velocity. You shouldn't expect much after that, especially when you're asking the bullet to penetrate engine blocks &c.
- oldman