Hello Bill,
The weight sounds fine to me. But if the edge is wrong, it is wrong. Originals have two matching overlaps exactly opposite one another. The edging machine always produces PAIRS of identical overlaps. As far as the details of a Mexico City edge itself - it is very REGULAR in size and spacings. The circles are CIRCLES not squares with round holes in them. The rectangles are RECTANGLES not squares and not trapezoids. The thickness of the edges are UNIFORM they do not vary all over the place. Other brach mints have some variation but NOT Mexico City.
So it is very likely a counterfeit. Boston forgeries made in the 1890s to the 1920s are silver of the correct weight. So if you have one of those it is most likely silver. In addition if it a very recent Chinese fake it MIGHT be silver. I have several that are made with Sterling silver.
So the next step is a Specific Gravity.