With out a chamber cast, you are working blind.

From Cartriges of the World.
"This cartridge was designed by Jeffery about 1898. It is a shortened version of the old black powder .450/.400 which has a quarter inch longer case. The two are not interchangeable. According to John Taylor in his excellent book, African Rifles and Cartridges, the short case was brought out because the longer black powder number had a tendency to stick in the chamber after firing. The .450/.400 Nitro-Express 3" was designed for smokeless cordite powder; it has never been available available with black. Prior to the .375 H&H Magnum it was one of the most popular and effective all-around calibers used in Africa."

Bullet dia .408, Neck Dia .434, Shoulder Dia .518, Base dia .613, Case length 3.00, OAL 3.75, Kynoch primer 40. It was loaded with 70 grains of Cordite. for MV 2150 and ME of 4930

http://www.cybertorpedo.com/africanhunter/classcart/450_400_nitro_express_01.htm

http://www.reloadersnest.com/frontpage.asp?CaliberID=154

http://www.reloadersnest.com/detail.asp?CaliberID=154&LoadID=10205

Pete

http://www.damascus-barrels.com/Movie.html