I am still not comfortable that you haven't confirmed your shooting a T/C or Ruger that can handle the pressure. However I will assume you are shooting such a gun. As far as heavy bullets go the biggest I have for my Ruger Super Black hawk is Lee's 310gr gas checked version that I cast myself. You have to see the massive meplat of this bullet! Its the biggest of all Lee bullet molds I am told. I actually haven't had a chance to develop a load for it yet but I will share what I know about such loads.
There are actually 3 pressure levels for the 45 Colt. Standard 14k psi max, +P at 21k psi max, and +P+ is around 30k. So the question, just how much power (recoil) do you want/need.
I don't care for that much recoil so I am going to try Accurate Arms data which is 15gr of #9. That gets me somewhere between 900 to 1000 fps with a 300gr (in my case 310, not that it matters) at only 19k psi so recoil shouldn't be that bad. Sorry about the wide velocity spread, but my Lee reloading Manuel and Speer Manuel list slightly different velocities.
If you want the max loads then your looking at H110/Win 296 (they are essentially the same according to the powder companies so reloading data can be shared between them) and Lgun are your main choices. If you go with H110/W296 keep in mind that powder really likes Magnum primers and high pressures. It burns very dirty at less than max loads. Lilgun meters better in most powder measures, doesn't require mag primers, and burns cleaner at less than max pressures. Its usually a few fps slower but definitely in the same power class as H110 though. It has a bad rap for heating up guns in high volume shooting, but in a T/C that shouldn't be a problem lol.
Report back with your range results, interested to know how it works out :-)