I thought this would be an excellent thread to post some scans from some old 19th century shooting and hunting books I have that discuss express sights and how to use them.

August Grimble's "Deer-Stalking" (1886), single best 19th century how to book on deer stalking. If you really want to see how 19th century hunters used their express/BPE rifles this is a great book. I know Africa gets all the attention, but the bulk of those 450 and 500 bpe double rifles were for stalking red stag in Scotland (and Indian game), not antelope in Africa.

I'll note my own Alex Henry rifle (1871) shoots just like the way he shows with the "Thick Sight".

From the living legend of 19th century shooting authors, Walsh "Stonehenge" and his classic tome, "Modern Sportsman's Gun and Rifle", (1882) a necessity in the library of double shooters in my view (better than Greener's book).

From the Philipps-Wolley's Badminton Library series on various sporting activities, from their volume on "Big Game Shooting II" (1894). This is from the chapter by H.W.H on "Notes on Rifles and Ammunition. Note, the Badminton library books are a wonderful intro to late 19th century British sporting activities.