gjw,
as everybody says Cyril launched a new era of classic guns appreciation, once you have read it, try to obtain Terry Wielands "Vintage British Shotguns" and Diggory Hadokes "Vintage Guns for the Modern Shot". Then you will have a fairly good picture of classic (British) shotguns. If you want to get further, then Vic Venters "Gun Craft" is the way to go deeper on several aspects of this industry this century and on how is also practiced in few other places. So far I have read trice Adams& Braden book and something new surfaces every time.
Regards,
EJSXS