Mystery 7th pin in Schlage mortise plug?

[prevariikation]

I have some mortise cylinders with a Schlage E keyway and 6 active pins, but also a (presumably inactive) mystery 7th pin. Originally I imagined it could interface with some type of cam, but the diameter of the pin is too large and seems to match a standard 0.115" pin. I'm guessing the factory just shaved down a plug drilled for 7 pins, and put a key pin in #7 to reduce the chances of bricking the lock during gutting, but I'm curious if there's another reason? Are there any 7-pin Schlage cylinders besides FSIC/LFIC?

[prevariikation]

A locksmith today suggested that the dead pin may be a key stop, so a broken-off tip can't fall out the back of the cylinder and interfere with the mechanisms behind.

[billdeserthills]

Baldwin mortise cylinders have the 7th pin holes drilled too

[prevariikation]

Baldwin mortise cylinders have the 7th pin holes drilled too

Ah, thank you, good to know!

[Raymond]

It might also be to prevent someone probing through the keyway to manipulate the inner workings of the lock.

[demux]

I vaguely recall seeing some videos where an enterprising person would put a 7th pin in that is actuated by the ramp at the very tip of the key as it enters the keyway. Only one depth is possible. Not sure if that's what you have here or not. An interesting thought though, however I don't think I'd trust it for a production lock. Such a scheme seems like it would depend on a level of precision in the key that you probably wouldn't find in anything in active use...