I happened to have come in possession of this one this past week. 54 caliber Ron Long locking system with 34" barrel.
aap-620_1 by Rick Mulhern, on Flickr
aap-620_5 by Rick Mulhern, on Flickr
aap-620_1 by Rick Mulhern, on Flickr
aap-620_5 by Rick Mulhern, on Flickr