It doesn't fit any of the types in what reference books are on hand, so it may just be an old chop job done for the civilian market.
Needs help, but the bore isn't bad.
https://www.milsurps.com/images/impo..._zps235d-1.jpg
https://www.milsurps.com/images/impo..._zps9090-1.jpg
https://www.milsurps.com/images/impo...34913707-1.jpg
https://www.milsurps.com/images/impo...a1a91687-1.jpg
https://www.milsurps.com/images/impo...df6964cb-1.jpg
https://www.milsurps.com/images/impo...03297763-1.jpg
https://www.milsurps.com/images/impo...b6917367-1.jpg
Just what was needed: Another project! :rolleyes: