I'd do some research and see if you can find load data for the particular weight bullet you're wanting to load. I actually thought that the .380 bullet diameter was different than the 9mm of .355, but Midway USA sells .355 bullets for .380, so maybe not.
At any rate, check your reload manuals or do some online research to make sure you have specific load data, powder charge weights, overall length requirements etc. Once you do that, happy loading, shoot straight and don't miss.
if you used the smallest grain 9mm bullet you could find like maybe a 100 to a 115grain you could probably get away with it.. the higher grain bullets are longer therefore there is even less case space for powder..
the guys over at the reloadbench forums load them as high as 124 gr with cast bullets but the loads are gun specific. many 380s cant handle heavy bullets lke that. a HP cold handle pretty much anything you caould make fit but a keltec or LCP would likely explode in your hand with the same loading.