Not being able to find a double lung shot deer that has been hit by a 7 mm mag does not speak to the effectiveness of the gun but to the lack of tracking ability of the hunter.
Or it simply means that the deer was not double lunged.I have helped out on a few long tracking jobs where the shooter assured me that the shot was right through the lungs.The funny thing is ,that in every single case,the animal was not shot through both lungs.The simple fact is,that if you don't recover the animal,you can never be sure exactly where the bullet struck,or what path it took in the animal.