Here is the entire text of the 2nd Amendment:

"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

What's the difference? The 2A certainly applies to cannons. Are those arms or munitions? Grenades are legal to own, just need the tax stamp.

I think the distinction is between "arms" and "ordinance". Reading through the comments here, it seems "munitions" is a super set of both.