From the Rüstkammer, Dresden:
"The South German rapiers with spring-loaded blade from circa 1570 are equipped with moveable blades which thrust forward and can be pushed back with a hollow metal handle. The blade is moved with two gears which take hold of the lateral cog on the ricasso. When pushing back the blade, the springs are tied around the core of the gears and thus cocked. When using the trigger, the blade springs forward some six inches."
Six inches is an awful lot of potential reach advantage to have at the squeeze of a trigger, but I'd think it'd be pretty obvious to see that one's opponent's weapon was so equipped...

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