I'm only slightly familiar with those two guns, but have some experience with similar revolvers. The actions of these, and many other European made revolvers, use the trigger as the locking bolt. As the trigger comes back to the cocked position, a projection on the trigger extends up through the frame and enters the notch on the cylinder. The hand, or pawl, that rotates the cylinder combines with this projection to lock the cylinder at the time of firing. Not too sophisticated, but its worked for many years.