Is This Cancel Legit

13? Line oval grid cancel on bisect on piece. If I owned it I would have to have it expertised by someone far more knowledgable, as I would be suspicious of authenticity.

It is very doubtful. Robson Lowe has a list of cancels, and oval types like this either have a clear open rectangle in the center or a clear open square at one end with a number. Not here. The bars and oval change from fairly narrow lines on the stamp to wide and less defined on the backing paper. The part of the cancel on the backing paper also has the quality of being drawn/painted; you can see what appear to be daubed spots along the bottom of the oval, which were then connected with overdrawing/overpainting in places. There is also what appears to be overdrawing/overpainting of the bars on the stamp itself. Examination under black light will then probably show differences between the cancel on the stamp vs. the part on the backing paper.