Be very carefully about what you see in museums, because alot of them say their item is authentic and this was Billy's or so-and-so's gun or possession and alot of it is incorrect. I use to work at a prominent museum and believe me I know the tricks and exaggerations they use to attract visitors. I have yet to know of one museum that has Billy the Kid's gun....oh, there's plenty that claim they have Billy's gun, but what I'm talking about is a museum that has Billy's gun with strong accurate provenance to support it. I don't mean to take anything away from you enjoying your sight-seeing and visiting of museums nor am I bashing museums, but because of my experience with some of them and working  behind the scenes, I now question anything I see on display or hear from a docent. 

As for Bob Olinger's shotgun, from what I know it's owned by James Earle and is on display in the Texas Rangers Hall of Fame in Waco, Texas.