Not intentionally made this weird though, mind you.
I had an MK1 Carbine around for a while that I never used, but I knew I could use an NBB sidearm.
So out came the tools (pipecutters mostly) and here was the result.
I didn't originally intend to leave the "handgrip" on, but the barrel was JUST long enough and it gives some extra stability, so why not?
In the end it turned out looking a little like a space gun. It's not quite what I had in mind, but it works.