I'm not sure their website is correct, at least not with the nomenclature. From about 1900, trapshooting was under the control of the manufacturers, the Interstate Manufacturers Trapshooting Association. Under a slightly different name, it was probably in action somewhat before. The Interstate Association (an abbreviation of the previous organization name with perhaps a different purpose), published an average book from 1913 to 1917. American Trapshooting Association took over in 1918. By 1923 or earlier, the recording organization was the Amateur Trapshooing Association and the Sportsmen's Review.
