I don't have one in front of me to actually measure, however, the exact length might vary slightly between manufacturer or even batch.
It's approximately .376" from where the bolt face sits in the extension to the face of the extension, so if you add that to 10.500", you get 10.876" (that includes the barrel extension).
I doubt it would be much (if any) shorter than that, could be a metric skootch longer?
How close of an answer are you looking for?