I looked in my COTW - I could find nothing called the .400 Purdey.

Unless - it is the 3" straight case, originally a BP round of the late 1880's - COTW lists that one as loaded with Cordite by Purdey.

It is listed as 230gr. cordite load of 47gr.- velocity 2,050fps.

Thus it is a bit less powerful than current loadings in the .444 Marlin. It would be splendid for any of the game the .44 mag rifles and .444 are good for - deer, bear, up to moose and elk at ranges to 200yards.

H4895 would be my choice, with similar loadings to the .40/70 Sharps to start with.

It should make about 1,800fps or 1,900fps with 350gr. bullets in a 'smokeless' rifle of good shape - or perhaps simply duplicate the .444's ballistics due to it's longer case, larger capacity at lower pressures, of course.(if twisted fast enough for the longer bullets)