This morning I picked up a Brazilian marked 1917. Took it out to the range when I got home, and while cleaning it just now, I came across a strange grind in the top underside of the frame, just behind the barrel. I dont remember seeing it on any of my other Smiths.

Is this something common? Nothing came up in a couple of quick searches here and on Google. Any ideas/thoughts?

TIA.

This is it here......