Very nice! The 404J is certainly a really cool cartridge.
Just a humble suggestion. I don't know their recoil limits but wonderful sight option would be tiny rail plus tiny Aimpoint dot sight with larger dot. I pick cheaper one w/o night vision device coupling capability. The when adjusted correctly the bullet goes where the dot is pretty much independent of stock weld and at appropriate dot intensity setting battery life is equal to shelf life of battery (thousands of hours)).
