A lot of us in Calif. are doing "featureless" builds because of new fooken semiauto rifle laws. Pistol grips, flash hiders are also verboten. You know, all the things that make them assaultive, dangerous and evil. The alternative is registering them as an assault weapon.
The length adjustment button, I used an idea learned here. Uses a aluminum threaded hollow wall fastener with an inserted setscrew. It fits inside the button and when expanded, keeps the button from depressing. A hole on the top of the button allows a hex wrench to turn the setscrew to shorten it and allow depression.