While watching reruns of Top Shot, it occurs to me that they have created some phenomenal video footage in slow motion of bullets leaving bores, gun motion in recoil, and gas clouds exiting barrels, at the least, from which we may conjure and opine.
I was intrigued by the first gas "puff" from the 45 ACP and revolvers upon the hammer hitting the primer and prior to the bullet reaching the muzzle. No truer empirical evidence for expanding gas obturating the bullet base to the grooves and "flame cutting" (mostly in cast bullets) than a video camera within the barrel.