The .45-90 originated as a sort of black powder express. The case length of the .45-70 was extended to hold more powder but original loads came with 300 grain bullets rather than the 405 or 500 of the .45-70. It normally utilized a slower twist rate also so may not stabilize the heavier bullets. The term Express does not seem to have been used much in the US is why I aid "Sort Of", but the concept is the same, IE a heavier powder charge behind a lighter bullet.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra