A deer shot through the heart/lung area with a Rocky Ti or a Thunderhead will die just as dead as one shot with the largested expandable on earth. I have to believe that the hits were not as good as you think.
Exactly. Either your shots weren' t where you think they were, or you need to go back and keep looking. Boiler room shots result in a kill with 100yds probably 95% of the time. Switching to mech heads definitely won' t help your situation. I' d be back out looking until I found them. Good luck.