Inspired by the reef 416d for your G5 GHK, it's equivalent to a GHK G5 12" CARBINE KIT.
A 5" 14mm external barrel extension supplied since 02/07/2023.
You will need a 300mm internal barrel.
I recommend the coated print with support on tray, to slide the g5 mount by disassembling the side rails.
The extension will block the reef.
License:
Creative Commons — Attribution — Noncommercial — NoDerivatives