Found this antiquing yesterday. Appears to have never been fired. No dents, scratches, etc. Heavy bugger, solid steel/iron from what I can tell.
81mm, WWII era. Only marks on the shell portion are two squares intersecting at the lower right corner upper left corner to form a smaller square and then a dot in the center of the two larger ones. Fin has SMP in two locations.
https://www.milsurps.com/images/impo.../jTDHpYd-1.jpg