Flatpointed or roundnose cast bullets were standard if not universal for scheutzen and benchrest at 200 - 300 yards. Paul Jones makes spitzer style .32 moulds, although the effort kind of fizzled in larger calibers. The pointy bullets are cataloged but seldom used.
There is no technical reason an 8mm-40 would not work; there were even period target rifles made or rebored to .33-40 for .338" bullets. The purpose was to get a heavier bullet at a reasonable length. Sectional density is not unlimited for cast bullets.
There is an economic reason. A GOOD .324" or so mould would have to be obtained, dies would have to be made or modified, and you might even have to have a chamber reamer custom ground. A common complaint of .38-55s is that chamber necks are too tight for a bullet made to fill the grooves. I don't know if the .32-40 shares that problem, but you should find out before you buy stuff.