The early writers Forsyth, Walsh and Greener all deal with the subject to some degree. I know of no recent writing on the subject. I am without my Library here, but as far as I remember, the system began with the Brunswick military rifle. This was used by many through the 1850's The idea was refined in 1852 by James Purdey into the "express train" using a small bore conical bullet propelled by a large powder charge.[4 drams in a .45 cal]. This basic theme was copied by many makers who also made large bore 2 grooves for dangerous game. The ultimate evolution of the 2 groove is the Lancaster "oval bore" produced until the 1930's.
All the best, Mal
