I've played with the 30-40, but only in several US Krag rifles and carbines. THE load for those I've shot has been 220 Hornady round nose and IMR 4350 to give 2100 fps, which duplicates the original military loading and seems to be quite suited to the Krag. A couple of 'em were rebarreled with new barrels, drilled and tapped and scoped, and both shot little "bug hole" groups at a hundred yards with the load.
I'm interested in your comment about a 1903 Model Springfield chambered to 30-40. Are you absolutely sure that it's a 1903, or a US Model 1896 or 1898 Krag made in 1903? I've got several "low number" 1903's, and have contemplated making a 30-30 or a 30-40, but then reconsider when I realize that I can dowload the .30-06 or shoot cast and get the same performance, and lower pressures in deference to the early '03's heat treat "problem".
I think that were I to come across the "right" Handi .30-30, it'd be a .30-40 in about two shakes of a lamb's tail!