SaltySteve,
Far too many new reloaders want to use only 1 powder for Magnum and non-Magnum rounds. Like said above, while it can be done both rounds will suffer. Slower velocity lower pressure rounds like the 45 Auto, 38 Special and 44 Special will be best served by a faster powder than high pressure high velocity rounds like the .357 Magnum and 44 Magnum. Magnum rounds will be better served by a slower burning powder.
Since you are going to use more than 1 pound of powder anyway, why not buy 2 different powders that will produce better rounds?
IMO, W231/HP-38, Clays, AA#5, Bullseye and Unique are good powders for the 45 Auto. For something a little hotter in the 45 Auto give HS-6 a try. (My favorite being W231)
IMO, W296/H110, 2400, AA#9 and Lil'Gun are good powders for the .44 Magnum. (My favorites being W296 and Lil'Gun)
If I had to pick only 1 powder for both I think it would be HS-6.
Have fun and be safe!