You can only do so much in 4-6", despite using faster burning powders in hangun loads. There is a lump of lead there, and when you try to accelerate it from Zero to Mach1+, you have to accelerate it at (for a 5" barrel) 220 Feet per second Per inch of barrel at an average transit time of 0.3 milliseconds per inch. That means you have to put, with a .01984 Pound 9/mm round, over 1.5 milliseconds, almost sixty Horsepower into that projectile.
I plead low coffee, if I slipped up the calculation, but still, it is an entertaining thought the next time you shoot a zucchini with Hydrashock..
After watching way too much Mythbusters, I'd really love to take a lot of different calibers and loads to a range and try them out. Dumpster-dive behind the farmer's market for a truckload of melons -- doesn't matter if they're spoiled, because they're not for eatin'. There's also a ballistics gel recipe I found online and would love to try.
Anyone know where I can rent or borrow a 10,000-fps camera?