You may try to shoot more thrrough the back of the shoulder blade. Breaking that bone helps get them down quick. Also, hitting that heavy bone will send it broken into the cheest cavvity increasing your wound channel. For this shot, you should go to a slightly tougher bullet like a Speer Grand Slam. I have switched to that shot placement when hunting game under 300 yards. Over 300, I'm not sure the 308 would get all the way through hitting the heavy shoulder blade. That does drop them better, IMHO. Sometimes chest cavity shots send them running for a short distance.