"Hammerless" centerfire shotguns have been around since at least 1838, Dreyse. Other commercially produced "hammerless" were 1850 Needham, 1862 Daw, 1866 Green, 1871 Mercott, 1875 Anson & Deeley.
In 1878 Dr W. F. Carver, an exhibition shooter, using a triple wedge-fast hammerless shotgun "shot upwards of 200 consecutive days, during which upwards of 40,000 shots were discharged from it" "This gun was used continually by Dr Carver for two years, upwards of 130,000 shots being fired from it"
"The first gun in which the weight of the barrels falling as they turn on the hingepin on opening thegun is utilized to cock the locks is the Needham gun". This was 1870. "The next mechanism was that of the Anson and Deeley gun, patented in 1875, ----- regarded as the first really successful hammerless gun."
Source of the above is The Gun & Its Development by W. W. Greener. 9th edition first published in 1910.