I'm sure we've had some June 15 1893 Horatio F. Phillips patent Vena Contracta threads but couldn't find them
https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA181&lpg

From From Atkin Grant & Lang website
After the move to 10 Pall Mall in 1890, Joseph Lang brought out the Vena Contracta gun, the brainchild of Horatio Phillips (shooting editor of The Field magazine), which fired a 12 bore cartridge in a barrel which was contracted to a 20 bore gauge during the first third of its length. However it was not a great success, as the weight advantage gained was offset by increased recoil and indifferent performance and many of these guns were subsequently re-barrelled.

https://sites.google.com/a/damascusknowledge.com/www/home