The other lug (camming lug) is situated on the upper surface of the barrel: it is engaged in an L-shaped cam track in the slide. When the pistol is fired, the rotational inertia of the barrel, the bullet torque and the slide's linear inertia (leveraged through the cam track) all act against the opening force of the cartridge.
The additional lug (camming lug), positioned on the upper surface of the barrel, fits into an L-shaped cam track within the slide. When fired, the barrel’s rotational inertia, bullet torque, and the slide's linear inertia (mediated through the cam track) counteract the cartridge's opening force.