I've used 2400 in my Marlin 1894 with the Bullet Barn's 240 gr. OK (and with Laser Cast before that) although I've not chronographed them. I believe 2400 was what Elmer Keith used to develop the .44 mag round. The Lee manual shows 20.6gr. of 2400 as maximum for a gas-checked 240 gr., for an estimated velocity of around 1500 fps- from a 5.7" revolver barrel, so add perhaps 200 fps. for a rifle. I don't have my loads handy but I think it's a bit below max. It does lead up a little.
The Lee manual shows 13.5 gr of 2400 as max. with a 310 gr. lead bullet for an estimated (pistol) velocity of 1150 fps.
I load H110 for jacketed bullets, but as I recall when I first tried it with plain hard-cast bullets, it leaded up the barrel and produced disappointing accuracy. The problem is that you can't reduce loads with H110 more than 3% or you risk detonation.
They don't show L'il Gun in their rifle data- only for pistol loads, where they show a max. of 17.7 gr. for a velocity of 1280 fps. from an 8" barrel, but that is for the 300 gr. Hornady XTP bullet; nothing is shown for lead. The max. load of 19 gr of H110 with the same bullet predicts a velocity of 1325 fps. They predict 1473 fps. for that load in a 20" rifle barrel, so that's close to your desired 1500 fps, but you might end up with excessive leading with un-checked lead.
I'm not sure why they don't show L'il Gun for rifle loads; it might be worth an e-mail to them. (help@hodgon.com) There also be newer info on their website. If you decide to try it, make sure you start 10% below max and work up.
Whatever you end up using, it will hit plenty hard.

Stuart