Identity of German mag box

[phoenix]

Any help would be appreciated in identifying this WW2 German mag box.I thought it was an unknown variant of box for the ZB26/MG26t, but it appears I was wrong (again!) It has got me stumped as I can't think of any magazine that will fit and also the strange layout of the box, with the middle section by the catch,is this space wasted? Please take a look at the attached pictures, thanks, Peter.

[phoenix]

Here are some more picture, including a standard ZB26 box.

[Adrian Stevenson]

Hi Peter, to be honest I was thinking ZB as well.

Cheers, Ade.

[phoenix]

Hi Ade,
The ZB mag I put in the box, in the picture, was a VERY tight fit and is obvously to short.
Peter

[Dimas]

French Chatelleraut 24/29?