What If rifle on Forgotten Weapons?

[Weaver]

Here's an interesting one. Even the highly knowledgeable Ian McCollum is in two minds about whether this is a real hybrid rifle or a fantasy what-if piece put together by someone having a laugh. He doesn't come to a conclusion so if you have anything to add, please put it in the comments if you can, or if you don't have a Youtube account, please feed it to me and I'll do so:

https://www.youtube.com/watch?v=VpbyBzx4VGE