I never thought I'd get involved in this discussion, but experiment of breaking the toggle with the recoil spring attached vs. disconnedted bothered me.
Try this experiment.
Remove the cannon from the frame (this removes the recoil spring from the equation). Remove the firing pin, to eliminate all spring influence. Insert a rod--pencil, whatever--into the barrel, and try to break the toggle by pushing on the breechblock face. Cannot be done, the geometry of the toggle train absolutely prevents the breech from opening. Turn the cannon upside-down, and the same result obtains. Incontrovertable proof that the geometry of the toggle train -alone- locks the breech.
You may find, in the inverted test, that the weight of the toggle knobs is enough to overcome the geometry lock, and lead you to conclude that the recoil spring does, indeed, play a part in keeping the breech closed. However, if you very carefully close the breech and handle the cannon such that the toggle does not fall open, the breech cannot be opened by pressure on the breech face (re-inserting the firing pin provides enough spring pressure on the toggle train to resist the force of gravity when inverted).
The difference is:
1. The geometry of the toggle train forces the breech to remain locked under -linear- pressure, -unless- acted upon by an external tangential force--the toggle ramps, hand operation, or the force of gravity.
2. The striker spring adds -additional- linear force to resist tangential force which may act upon the toggle train.
3. The recoil spring resists -rotational- motion of the rear toggle piece which occurs once the linear geometry of the toggle train is changed.
None of this, by the way, is intended to explain the forces and actions which close and lock the breech [img]wink.gif[/img]
--Dwight
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