The .45-90 Express is a modern adaptation of .45-90 Sharps which uses the same 2.4 inch case, but uses smokeless powder loaded to pressures up to 45,000 psi.
Many modern nitro-proofed single shot or break barrel .45-70 rifles can be easily reamed by a competent do-it-yourselfer to shoot .45-90 Express.
When used in modern repeating firearm such as a converted Marlin 1895, Enfield, or Winchester 1886 the cartridge overall length of the .45-90 Express needs be kept to under 2.85 inches to reliably cycle through the action.
The .45-90 Express is well suited for hunting the largest predators including lion, grizzly, and polar bears, as well as moose, cape buffalo, bison, and elk.
The Complete Blackpowder Handbook, 3rd Edition by Sam Fadala, Krause Publishing, 1996, P. 247