Considering Chris is an autistic manbaby, he is probably afraid of guns, the loud noises from firing might scare him by themselves. And IIRC he backed down from visiting Megan once he found out she owns several guns!
But even if Chris decided to overcome his fears and own a gun, I doubt he would be that dangerous. He runs on child logic combined with movie logic, presuming he would even know how to effectively use a gun is putting too much confidence on him and he would also probably keep it in a shit state, good luck firing the pistolchu when it's crammed full of dust, dirt and fanta lol!
Chris wouldn't understand any of these as well. He has trouble grasping the concept of the existence of certain places, can barely use money as is, try explaining to him that he is now under a restrictive ruleset that is far more severe than being banned from a store. He would probably ignore the restrictions within a week!