Assigning makers by vitue of the shape of an action is somewhat problematic. For example, here are what I would call fairly typical Dan'l Fraser double rifles;

Firstly a BPE;

and a pair of typical .303 doubles;

None of them look like the so-called typical Leonard/Jeffery/A.Hollis rifles shown elsewhere in this thread!

Now, here is a Jeffery rifle attributed to Leonard, from your source, "Birmingham Gunmakers" by Douglas Tate;

Note that flat action back - a bit different to Rusty's typical Leonard rifle??? In fact, I once owned a Jeffery rifle that was identical to this rifle, and it was also a dead ringer to a Wilkes .470 that I believe is currently in the possesion of another poster on this forum.

Upshot of all this?? IMO - attibuting "gunmakers" on the basis of the shape of the action is fraught with danger.

BTW - Donald Tate was born in Newcastle-on-Tyne, England and worked in the graphic arts industry in London, Sydney and New York until he was 40, after which he became a Seattle-based Gundealer. A knowledgeable man he might be, but I would have liked to see more acknowledgements of his source material in his book, rather than simple regurgitation of some "urban legends" that have been put about, particulaly by some US based "gunwriters"!