So, his other gun then. Not standard Judge issue weaponry and not based on anything i can remember from the strip, so what to do?
Did consider not using it and either replace with a robots head (nixed that as i'd need the rest of the robot on the base to explain what he's doing with it and that'd make for a VERY busy base) or scratchbuild a Stubb Gun (nixed that as the time Joe used one was in the Apocalypse War, way before his MKII Lawgiver was issued).
So decided on going the route of sticking with the gun, but having it nothing to do with him - he's picked it up mid-battle for some extra firepower.
To emphasise that i've made it a Perps weapon, with a colour scheme different to any Judge issue item, and rusty as heck.