I think the Shumway write up and his placing it after the Valentine Fondersmith rifle and noting the similarities is all I've ever heard on the subject. Interesting that the VF rifle looks earlier in patchbox design but the JS rifle has the wider buttplate. Guards look like they are from the same master, carving identical, similar unusual cheek piece rear transition, etc. Somewhere there are listings of Lancaster gunsmiths you could check. I seem to recall Fondersmith shows up on Lancaster tax rolls etc.
