Below is a link to a 2018 video by Dave Geiger featuring a J. Graeff signed rifle that I believe may be Lot #1100 in Morphy's up coming auction.
There were two "J Gaeffs" building rifles in the town of Lancaster, brothers John and Jacob. Thus far, none of the extant "J Graeff" signed rifles can be assigned to either brother. Bob Lienemann and Scott Gordon have performed excellent research on the Graeff brothers and were kind enough to share it with me. There was a John William Graeff stocking rifles in Berks County but none have been identified to date. Dave Madary discusses J. W. Graeff in Part Two of his three-part articles appearing in the recent KRA Bulletins.