Mr. Janacek was a Czech designer and his principles incorporated a rifle with a standard barrel, but with a tapered bore muzzle attachment which could be easily unscrewed and replaced. The bullet worked on the almost the same principle as the Gerlich bullet which was swaged down when passing through the muzzle attachment. It differed however in that the bullet had a collapsible outer body that folded in upon itself instead of skirts like a Gerlich bullet.

close up of the headstamp marking