MPX Bolt Carrier loose "gas key"

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February 13, 2020, 08:40 PM
MPX Bolt Carrier loose "gas key"
I recently inherited a 9mm MPX. While cleaning I found that the piece that attaches the operating rod to the bolt carrier is loose (it's analogous to an AR gas key, not sure what the proper name is). Should this piece be loose?

February 14, 2020, 06:45 AM
El Cid 92
Mine will "wiggle" a bit. But does not slide out from either side. No issues with function.


Duty is the sublimest word in the English Language - Gen Robert E Lee.
February 14, 2020, 07:02 AM
I would be curious to know whether it’s something to be concerned about because I’m not familiar with the MPX. It appears to me, though, that the part (that SIG evidently calls the operating “rod”) is held in place with just the roll pin, and is therefore probably not intended to be fixed rigidly in position. Perhaps it is designed to shift slightly to allow it to self-center in operation. The similar part in the MCX is not fixed and has a relatively large range of motion.

“The fundamental cause of trouble in the world today is that the stupid are cocksure while the intelligent are full of doubt.”
— Bertrand Russell
February 14, 2020, 02:31 PM
To clarify the movement is a bit of play and the piece does not come out on either side. I don't expect that it will affect function as the carrier's motion within the receiver is limited.