You already know about COTW and Taylor. Another good reference book is "The History And Development Of Small Arms Ammunition-Volume Three" by George Hoeym. This volume covers the British Cartridges, and although there is no extensive coverage of any one caliber he does offer a broad range of calibers, some of which are not listed in the common references. Another good reference guide is "The Handloader's Manual Of Cartridge Conversions" by Donnelly. This has dimensions for many factory and wildcat calibers from around the world, plus a few loads for many of them, and the easiest parent cartridge for forming cases for each.

Jim