Hi,
There were several kinds of patent breeches. The simplest just have a powder chamber as you describe. The purpose was that the small amount of powder in the chamber would ignite and then provide sufficient heat to ignite the majority of the powder charge which was in the barrel instantaneously. That increased the power of the explosion for a given charge of powder compared with a simple flat-faced breech plug and the total charge ignited by a small flash through a vent hole on the side. The result was a gun that shot harder. However, a simple chambered breech does not increase speed of ignition because the touch hole or vent leading to the narrower powder chamber has to go through thicker barrel wall. That problem was worked out by Nock who included a small antechamber for powder that actually was oriented perpendicular to the bore but connected to the powder in the barrel by a channel. Along with a coned vent liner, the antechamber brought powder close to the flintlock pan speeding up ignition. The powder in the antechamber then flashed and ignited the main charge in the barrel instantaneously giving the same performance of power as the simple chambered breech. Other gun makers solved the speed of ignition issue by cutting out, or stepping, the lock side of the breech allowing the pan to be close to powder in a the small powder chamber like the simple breeches rather than a perpendicular antechamber like the Nock. These produced fast ignition and greater power.
dave
