I'm also disappointed by this story.
Please learn from the experience.
The front sight post on your M1 Garand is approximately 8-10MOA... it depends on your eye relief from it and how much glare or how bright it is.
It should be approximately equal to the width of a man's chest at 200 yards (20 inches).
That's about 1/3 the horizontal width of an elk.
I'd hope that from field positions, you can muster an 8MOA shot. That will go into a 16" circle at 200 yards. While your optimal kill zone on an elk is a bit smaller than that... 8MOA should do it out to 150 yards as you describe (which would be 12" in diameter at 150 yards).
I understand that you were putting down a sick and abandoned animal... but you had plenty of time to put it down properly with a competent shot.
I hunt with an M14.
But... If I heard a Garand get emptied in the woods where I am hunting, I'm packing up and calling it a day. Just because it's an autoloader doesn't give you license to send bad shots out.