Lee440:
I had an idea that someone had answered this for you already, if so please disregard my post.

The JA in a circle indicates that Joseph Asbury made the barrel group. He was primarily a barrel-striker, but may have been an action-filer as well, my own library is unclear on this. Perhaps Asbury made the barrels and 'HR' built the action.

As an example, my Manton .470 was built by John Wilkes, however Josh Asbury struck the barrels. The gun retains a shadow of Wilkes' name in the case-colours on the flats (the original stamped name was struck-off prior to case-hardening, but the bruised metal coloured differently), and Asbury's 'JA' in a circle is present on the barrel-group.

Now to concentrate on 'HR'!

Fascinating stuff!

(edited to change Asprey ot Asbury, and delete references to Asprey double rifle thread)