This reloading topic along with the "A little hard to conceal!" thread over General Gun Discussions area got me to thinking about a load development (working up a load) test, for a naval gun, I was involved with.
My memory is a little fuzzy, since I wasn't directly involved, but as I recall, the goal was a 120 kg projectile at around 850 meter/sec. I think they ended up with around 28 kg of powder.....!
For you reloaders, I think that is about a 1,800,000 grain bullet at 2,800 ft/sec, over 430,000 grains of powder!