I think it means, if you aim at a small part of something you want to hit, and you miss that spot you will still hit the Target as a hole.
For instance: If you aim at a human eye ball, shoot, and hit between the two eyeballs you "missed small" Get it?
I guess I should Clarify My Handle "MT GUNNY", I was In the Army and I do have knowledge of Infantry Tactics.
But that is not why a Use it. "Gunny" I see as a all around term for Someone who is Knowledgeable in firearms, By no means Expert!
Gunny is also a term The Marines Use for a Sergent Rank. MT is obviously for Montana.