This is a very well used Adams Model 1872 revolver. Chambered in the British military.450 Boxer cartridge (also known as .450CF, .450 Adams & .450 Eley). This revolver is the commercial version of the British military Adams Mark III revolver. 

Very faintly marked on the right side of the frame is ADAMS PATENT No. 9176 along with the  John Adams trademark.. The top strap is marked ADAMS PATENT SMALL ARMS COMPANY, 391 STRAND, LONDON.