I finished up my P-47D and am moving on to what will hopefully be my first completed tank can not find a reference on how to give a crude cast effect for the turret? any help would be great.

Apply extra thin liquid cement then stipple with a stiff brush after a few seconds..

H , if you use a dremel to rough up the surface first then paint the glue on and stipple with an old toothbrush , you will end up with a rough finish .
To add extra detail to the turret , the m/g ring at the rear can be recessed into the turret or it can be proud of the surface . Or it can be the full height of the rear face. You could add the casting lugs under the rear bussle for yet an other version .
plenty of ref out there just needs searching for good luck ian