There is an interesting short video from the Smarter Every Day series on YouTube about the development of a very fine measurement instrument by Joseph Whitworth and within this story is another story about the Whitworth guns/projectiles and slow motion videography of firing a Whitworth breech loading rifled gun!!!
From the video-
U.S. Civil War Whitworth rifle bullet, dropped and found 100+ years latter with a metal detector
Modern functional replica of a Whitworth breech loading rifled gun
Projectile for the modern Whitworth gun
Screen image capture of a high speed video showing a modern Whitworth projectile being fired from the replica Whitworth gun at just over 1000ft/second