From the OP:
"i got a small Cow down after 2 rnds from the '06 at about 200 yds." He later explained that this was with hunting bullets, not GI Ball.
"...about 15yds from her she jumps up and trys to take off! with my M1 slung in a backpacking stile i decided to give my 45 a go on her...first two i missed the third shot knocked her over."
"i found the third lodged in her lung wile gutting her. and the fourth for insurance one to the head because she was still kicking a little bit."
I grant that this was not the easiest post to parse that I've ever seen. However, I don't quite understand all the fussing and snark.
Seems to me that the .45ACP performed admirably in this rather unusual circumstance. The reason for the use of it looks like a logical decision at the time.
More: The brother is the one who wounded the elk. It turned out that the elk had been previously wounded, which is irrelevant to this thread. So the result is the prevention of escape of a wounded elk, and yet people are griping at the guy who did the proper thing?
All of that is separate from the OP question about the actual suitability of the .45ACP in more normal circumstances of hunting elk. I think it's reasonable to say, "No, don't do that."
You're from BATFE? Come right in! I use all your fine products!