Every once in a while I hear someone mention that a case design is more efficient or less efficient than another. A 22 K Hornet is more efficient than a .22 Hornet. A Gibbs design is more efficient than an Ackley (or vice versa). Well what exactly does this mean? How does the shape of a case change the efficency? (The powder burns and pushes the bullet down the bore. What does the powder care what shape container it's in?) What benefit do I get from an efficient case?