A firearm stock extension assembly enables a stock to be collapsed when a firearm is not in active use, and extended from a collapsed configuration directly to the user's preferred stock length. This is accomplished without requiring the user to actuate a lever to release a detent mechanism and without the need for hand tools to adjust the length of the stock. The firearm stock extension assembly includes an insert that defines at least one insert aperture. When properly placed, the insert aperture of the insert lines up with a corresponding extension aperture on the stock. Other than the corresponding extension aperture exposed by the insert aperture, all other extension apertures are concealed by the solid portions of the insert.