My 45 has a long chamber but a very short throat. I can not fit in a 454 (almost closes) but I can fit in a 450 extreme. This cartridge is described in a few places most recently the 2009 Hodgdon Magazine/Catalog, and is somewhere in between Colt and Casull. However I can only fit in certain bullets because of the short throat when I do this. A Sierra will generally go right up to the lands, but many Hornady's do not at least not crimped in the groove.
Favorite load is a 454 case shortened to 450 extreme length, with a 200 grain Hornady FTX with the case full up to the base of the bullet with H-110 (actually surplus 820). Using a BR4 primer, a little high at 100 and a little low at 200 and about 1.5 MOA all day long. Using ridiculous amounts of holdover I have hit the 400 yard gong at least once in a batch of 50 reloads, (ridiculous grin). Becoming a faovorite as eyes and arms fade and it becomes more "Handi" than the Freedom Arms it will replace someday.