I know that the German surnames Kerchner / Kirchner are completely different German surnames than Kershner / Kerschner / Kirschner, but I thought I would tell you about my new Y-DNA project.
I have started a new project using science and genetics to try and aide with my genealogical research of my surname, and similarly spelled surnames. To learn more about it, visit my Y-DNA Project website:
Possibly some direct male Kershner / Kerschner / Kirschner descendants would want to participate to establish a Y-DNA profile(s) for the family name with the "S" in it. I would be happy to track the results of participants for your surname, for comparison with other participants, via my Y-DNA website. Details on how to participate in my project are found in the Y-DNA website, linked above.