Hugh,
Thanks for the information on No.7116. I am currently restoring
No.7193 (Powells Patent 2312) -- a 12-b bar-in-wood Best hammer gun. The Powell ledgers show that the gun was sold on August 28, 1880 for £30. The Powell records don't include patent use information.
All of the forend latches I've seen to this point were either wedges or Anson's.