This is an adapter that I created for the Nerf Retaliator. It allows for the removal of the priming handle and allows for the installation of a pump grip primer.
I printed mine with three layers on the walls giving a total wall thickness of 1.2mm. It is designed to be used with 1/2 inch flat stock with an 1/8 inch thickness and M4 nuts and 12mm M4 bolts.
The second version does not have a cover. There is a 6.5 mm offset down and 15 mm forward. It works better with Magnus Pump kit.