He's very lucky to not have had his head hanging over the magazine when that went off. Idk if there would be enough velocity to kill, but that's a big piece of lead moving down the pipe at 900 fps. It's going to leave a mark.Completely possible and he did it.
The rifle (as I quoted) was an1860 Henry Rifle 45 Long Colt. You can drop a cartidge in up by the muzzle and have it fall the full length of the magazine. Once the first cartrisge is there the next one has the primer landing on a bullet... hopfully a flat nose, but in this case he loaded bullets with a round nose.