The United States Army’s Redstone Arsenal requested a rifle cartridge that could develop 6,000 ft/s (1,800 m/s) for the effects of light bullets against armor. The .30-378 Weatherby Magnum was able to attain over 5,000 ft/s (1,500 m/s). A while later using a slower burning denser propellant the .30-378 Weatherby Magnum surpassed the US Army’s requirement of 6,000 ft/s (1,800 m/s).
How is 6000 fps possible in the ballistics world? Isnt ~5000 fps the top limit for conventional propellants? If not, what are those bullets made of if they can hold together flying faster than a mile per second? What was the bullet weight too? Even a 40 grain bullet has more energy than a .30-06 at those velocities! Conventional 147 grain M80 ball bullets would almost hit .50 BMG power!