Thanks, I appreciate the responses.
At this point I am leaning towards a simple - '.303 CARTRIDGE'
interesting, this rifle has the address;
GEORGE GIBBS, 29 CORN STR, BRISTOL
I thought that Gibbs vacated those premises in the late 1880's and the .303 British only become available in the early 1890's.
Slight discrepancy there!
Charls