Well, I know it's an AK47 magazine because I have AK47 mags for visual reference.
The problem I see with this rifle is mainly twofold. First, it lacks a forward handguard, and I know from experience that you DON'T want to be grabbing at the barrel of a rifle once you empty that magazine. (I had barbarque marks on my hands for several days as a result of this lesson.)
Second, I see nothing resembling enough room for a gas rod, meaning that the action will be blowback only. Even in the 1930s direct blowback is getting known as the wrong way to go for a rifle-caliber semiauto.
Bullpup rifles of this generation are going to have a lot more mechanical problems. There's a lot of difficulty because the trigger is now in front of the action and the connection has to be bridged, adding mechanical complexity. Add to that the fact that you'll need an intermediate round on that rifle, of which only two exist in WW that I know of - the German 7x40 being one of them.
For me, though, the lack of a gas return operation makes me suspect of this rifle being very useful. Now, if it was an SMG with a pistol round, then direct blowback would probably work well for the size - but then I'd have to question the reason for a bullpup SMG.