John - Many thanks for posting, as I said before, a very interesting rifle

The only similar Field's Patent I am aware of with reinforcing plates/strips is also in Jonathan Kirton's book, retailed by Rigby and made by W&C Scott

As W&C Scott made many of H&H double rifles (including both of mine) prior to the 1892/3 factory build I am reasonably confident your action at least (probably the whole rifle) was made by them

The rifle could have been originally (from the date) .303 but equally one of the .450s or even larger

The wide top rib is a good indicator of a better quality rifle

I particularly like the Field's Patent as it is easier to use for me than the underlevers (Which I also like!!)

Good luck with your shooting

Tony