As the bullet travelled down the barrel after firing, it eventually passed a hole drilled in the bottom of the barrel known as a "port". The hot gasses behind the bullet flow into the port and push down on a plug, marked "p" in the diagrams. This causes the plug to pop out of the hole with some velocity. The plug is attached to one end of a short lever, "l", the other end of the lever is connected to a hinge below the barrel. The motion of the plug causes the entire lever to rotate down and to the rear, around the hinge point. This action is essentially front-to-back version of the typical back-to-front motion of a lever action rifle. The end point of this motion can be seen in the lower diagram, with the lever having traveled through an arc of about 160 degrees. A spring located at the hinge is compressed by this motion, and eventually causes the lever to rotate forward again, forcing the plug back into the port and holding it there when it is not in motion.