Thanks for the videos. I'd never seen that type of file. I use a regular file, and I push for a while, then pull, so as to not get my arthritis worked up. I don't go at it with anywhere near the finese you show though! I look more like a monkey trying to open a coconut. First this way, then that, turn the music up, wipe your brow, more coffee, and poooof, it's done!
Draw filing and cleaning up my castings is my first step building a gun. It definitely helps the barrel slip in and out more easily of a nice tight channel.