Here are a few points about the F4U-1D and 4.
1. The 4 20mill cannon load was an option interchangable between aircraft. Not production only.
2. While the 20 Mill gun installation was 35lbs heavier than the 50 cal machine gun intall the ammo was significantly lighter as was the aircraft.
3. The F4U-1D could takeoff with more than a 17,000LBS gross weight. We are limited to slightly over 15,000lbs.
4. The F4U-1D and F4U-4 had an interceptor loadout that included 178 gallons of fuel and half ammo load of 1200rounds.
Here are the docs
