The boxes are different, Mike P is looking for a Locker, Ammuntion.
To quote the handbook:
The No.2 ammuntion locker, employed with the mark II carriage, is an aluminium alloy rectangular box with hinged door at the rear.
The box is divided by a shelf into two compartments for containers and internally has riveted to it eight bearing strips for the containers to bear upon or against.
The inner rear face has solutioned to it a sponge-rubber pad, while the inside of the door is also padded with rubber to act as cushions for the containers. The rear end of the locker has two hinge brackets and a strengthening plate on top for the door.
The door has a handle and is fastened at the bottom by a quick-release lever and link attachment, the lever pivoting on the door, while the link pivots on a bracket secured to the underside of the box.
On top are four housing studs for the tool case, while on the underside are four screw-threaded studs with nuts to hold the locker to the carriage.
Tigbrands box is a 'Box, Ammunition, Q.F. 2-PR., C.207'
Both boxes when filled held two 'container, Ammuntion, Q.F. 2-PR. Marks IX and X Guns' which hold eight complete rounds.
Hope that helps.
Quatermass