You could ask Billy.
PTSD for a veteran is considered a service connected disability by the Veterans Administration. Whether or not the veteran was obsessed with guns before or after their service or not at all is irrelevant in that determination. The VA does and will treat extensively for PTSD and for obsessions of about any kind. I believe that the question by WB can be answered in a manner that he will probably not like but it can happen in any number of ways and times. Life's a bitch, don't you know? In any event it's a disease and a very dangerous one.