It won't chamber PROPERLY. It will go in, go off, not blow up the gun, and launch a bullet in the general direction of interest. It is something that used to be done so as to say you had shot Grandpa's rifle or to shoot a once a season deer at close range. It is not something to plan on like shooting .38s in a .357 revolver. Brass is available if you are a handloader and ammo is available if all you want to do is fire a few rounds to be able to say you had.
A good .45-90 is quite accurate; a friend has one that can suprise the guys with their plastic stocks and Chinese scopes.
Some say a .45-90 will shoot a 405 grain bullet well enough, but don't count on it, the rifiling twist is quite slow for the standard 300 grain bullet.