Install the bushing into the end of the barrel. Don’t tighten it all the way until the gun is fully assembled.
Remove your existing rail by using a 1/8″ hex key to remove the hop adjustment screw and 8 retention screws. Refer to the Owner’s Manual or Disassembly Guide Video for detailed instructions. Be sure not to lose your hop nub when removing the rail.
You can re-use the hop-adjustment spring and detent from your existing rail or use the spring and detent that came with your new rail. The spring should be cut a length of approximately 1/2″ (13mm) if it hasn’t been already. The spring is installed first, followed by the detent.
Slide your new rail onto the Gen-12 and reinstall the hop nub (oriented vertically) and hop adjustment screw. Ensure the hop adjustment is engaging the spring and detent and clicking when turned. Secure the rail with the 8 retention screws using a 1/8” hex key. Fully tighten the bushing.