I'm with HiBC on this one. If you do enough research you can probably find a 45 ACP load that might work on an Elk. Shooting bullets into water to me proves diddly squat. I will remain skeptical that there are loads appropriate to being fired from a semi-auto in 45 ACP that have the energy and bullet construction to not only penetrate deep into an Elk but also cause enough tissue damage. To me I think the 45 ACP will either sail through an Elk with FMJ and cause little damage or not penetrate enough with JHP if they expand.
I will have to disagree with Brandy that the size of the bullet is all that means anything. If that were the case the 380 ACP is just as good as the 357 Mag as a hunting or self defense cartridge. A 30-30 is every bit as good as a 30-06 or 300 Win Mag. That of course is absurd. Anybody educated on the matter knows that the 380 ACP simpy isn't as effective as the 357 Mag. The Magnum will penetrate and expand better and do much more damage than the 380 ACP. Comparing the 45 ACP to the 44 Magnum or a large caliber rifle is like comparing the 380 ACP to the 357 Mag. Or like comparing the 30-30 to the 300 Win Mag.
IMO, the only 45 ACP loading that will reliable penetrate an Elk is FMJ but I would strongly suggest that it would take the Elk quite a while to go down. As has been seen in autopsies, FMJ from handguns is very poor at wounding, regardless of caliber. Brandy, there are criminals that have soaked up a magazine of slugs from a 45 ACP and took a while to go down. An Elk is an entirely different beast. I'm having a hard time believing that a commercial ammunition maker would develop a self defense loading that would penetrate that much.