Uncle Wray,
I've killed SEVERAL elk from bow distances to well over a hundred yds with a .44 mag, .45 Colt and the Casull. You can do it cleanly with a .44 magnum handgun. I use my own handloads with 275 or 300 gr LBT's in the forty four.
Federal loads a 300 gr CastCore lead load that would be PERFECT for Your situation. I'm not speaking from internet knowledge but practical knowledge. Even a 250 gr Keith slug at a mere 1100 fps will shoot right THROUGH a mature bull. I've done it! The penetration of a hard cast slug at a moderate speed from a .41, .44 or .45 handgun will AMAZE you.
DO be aware of whats BEHIND your intended victim. I once did a two for one "trick shot" on mule deer that turned into a real mess. Only had ONE tag!!
FN in MT