Rich,
You didn't say what gun you are using the load in. For 'standard' .45 Colt loads, ie Colt SAA and replicas, Alliant lists 12.5 gr. of 2400 with a 300 gr. Hornady XTP for around 700fps in their freebie manual.
In the Hodgdon #26, page 589, for Ruger/TC/Dan Wesson/Anaconda and similar high-strength guns, a starting load is listed for 300 grain bullets (type not specified) of 18 grains of 2400 for ~1,000fps at 25,000CUP, and a max load of 19.5gr. of 2400 for ~1150 fps. Barrel length given as 7".
You might know this already, but for 30,000CUP loads in the .45 Colt, either H110 or WW296 will probably work out a lot better. I say this because at the lower velocities that you get with 2400, you might not have a tall enough front sight.
Hope this helps. If you can find a copy of Hodgdon #26 it is well worth the price for the .45 Colt shooter.
<!--EDIT|MikeG|Feb. 15 2002,22:14-->