An HO scale, 1/87 Sherman tank turret from Paul Heiser Models. this is the mid-production 75mm gun version. It has the oblong loaders hatch opening.
This is the T-23 turret with loaders oblong hatch. The indent shows where the hatch goes, it lays flat on the roof to avoid a shot trap. Paul has made these masters using resin copies of his own models, bits of plastic from his own kits and masters he has carved.