When the main-spring tension screw is free, remove the main spring, and then the
hammer, and then the cylinder assembly, and then the cylinder release mechanism.
Now you can double-action the trigger, and you will see how it compress's that
secondary spring. You can make a little piece of wood, or brass, that will catch,
on its upper end, in the end of the slot for the cylinder release slide. The other
end should catch that second spring, just below that levering piece. You fit this
tight with the trigger fully pulled pack. This will hold that rebound spring down.
You can now release the trigger, and lift out the whole assembly.
Now - if you want, take a pair of pliers, wrap the end with tape, and catch hold
of the end of the rebound spring. Tighten up, and that holding piece will come free.
Release the pliers gently. If you want, but its not necessary, you can remove
that rebound spring. Generally, its not necessary to take it out.
To reassemble, compress the spring with the pliers, put back the temporary retaining
pin, and then drop in the trigger assembly. Squeeze the trigger enough to release
the holding pin, and then reassemble the rest of the lockwork.