I think if I were in your shoes I would have to point out his total lack of knowledge on the subject of rifles, ammunition and ballistics. Wether it made him feel like an idiot or not is none of my concern. He should have a basic knowledge of what he is teaching.

Speak up. It's not your fault that he doesn't have a clue. Maybe you will save someones life because you pointed out the difference between a 7.62X39 and a .308.