G.T. Teasdale-Buckell
Experts on Guns and Shooting, 1900
In the Advertisement section
https://books.google.com/books?id=4xRmHkr7Lp8C&pg=PA597-IA12&lpg Charles Rosson "INVENTOR OF THE ORIGINAL TRY GUN" 
Then scroll down in "Introduction" and Rosson is discussed; he apparently did not patent his try gun
https://books.google.com/books?id=P7UrAA...p;q&f=false "Rosson, of Derby, deserves special mention. He saw the necessity for a try gun, which he invented but did not patent in 1876, and this gun,
along with Mr. Oliver's (at Haymarket), prevented the Jones patent becoming a master patent."
p. xxii list of gunmakers the first try gun is attributed to Rosson
Mr Purdey is unimpressed
https://books.google.com/books?id=P7UrAAAAYAAJ&pg=PA28&vq "The Use and Abuse of the Try Gun"
https://books.google.com/books?id=P7UrAAAAYAAJ&pg=PA102&vq https://books.google.com/books?id=P7UrAAAAYAAJ&pg=PA69&vq Beesley's
https://books.google.com/books?id=P7UrAAAAYAAJ&pg=PA312&vq Churchill
https://books.google.com/books?id=P7UrAAAAYAAJ&pg=PA346&vq Holland's
https://books.google.com/books?id=P7UrAAAAYAAJ&pg=PA406&vq https://books.google.com/books?id=P7UrAAAAYAAJ&pg=PA471&vq https://books.google.com/books?id=P7UrAAAAYAAJ&pg=PA513&vq 
