I try to get hunters that I guide to shoot the lungs. 4 reasons, one it kills the elk, two I get a blood trail, three I have seen a lot of elk shoulder shot and run out of the country, 4 it offers a huge kill target.
In general, if you hit an elk hard in the lungs, the animal sort of freezes and shudders, and offers a second shot. again, shoulder shots that break a single leg will have the animal off to the races. I have video on this very thing,
hardpan
This happens so frequently as to be a maxim. The only animal I've seen that can move faster than a elk with a broken shoulder is a grizzly with one broken shoulder. They can move amazingly fast.