Some people may know the 37mm McClean automatic gun which was made in small numbers during WW1.
Recently I came across this image showing an essentially larger McClean gun which also is automatic (note the chute for the clip). Caliber might be 47mm or 57mm.
Is anybody able to ID the caliber/cartridge that was used in this gun?
Of course details on the gun are also highly welcome.
Image source: internet.