WPboatr, the cylinder is kept from being pulled off the center pin by a flat plate with a lip found under the latch. The lip is pointing downward and serves as a stop when the cylinder moves backward. On the top strap of the gun just in front of the latch is either a round head screw or a knurled knob depending on which issue of the #3 you have. That has to be loosened to let the cylinder catch move upward to allow the cylinder to clear. You can see it from this picture of my Russian #3, 3rd Model.
