I think what I find so curious is not simply that it's a step wrist / toe, but the shaping of the stock in conjunction with the step. Looking at the mortises for the missing furniture, my 'dating estimate' would probably be 1790s. However, in that case, even if made up in the Lehigh area despite the Bucks furniture design, I would expect much more curvature to the stock like a Moll or Rupp rifle. Yet, this step-stock looks awfully similar to an Oerter stock or something of that 1770s era. It just makes it weirder than it already is!
Also looks really red, like a colored varnish. Original? No idea.