Remington AccuTip 20ga

I recently bought a Savage 220 slug shotgun. Since everything I read about the gun in forums and Savage's own manual said to use Remington's AccuTip slugs for best accuracy. I bought the AccuTips, sighted in the gun, and was very impressed with the groups it shot. The problem....I shot two deer with this ammo and was a little disappointed in the results. Both deer were shot thru both lungs, showed no sign of being hit, and ran over 150 yards before going down. When field dressed, it appeared from the size of the entry and exit wounds, that the slug had not expanded at all. Since the slug is approx. .45cal. I was expecting better terminal results. I'm interested in other hunters results with this slug.