This isn't objectively true, as evidenced by the decision in US v. Miller. I (and many others) believe that decision to be flawed, but here it is:

> In the absence of any evidence tending to show that possession or use of a "shotgun having a barrel of less than eighteen inches in length" at this time has some reasonable relationship to the preservation or efficiency of a well regulated militia, we cannot say that the Second Amendment guarantees the right to keep and bear such an instrument. Certainly it is not within judicial notice that this weapon is any part of the ordinary military equipment, or that its use could contribute to the common defense.

In other words, they held that the weapon in question was not covered specifically because they did not believe it to be military equipment. It logically follows that "ordinary military equipment" is what is protected by the Second Amendment.

Yet pre-1970 the NRA itself was one of the staunchest advocates of licensing, gun control, and restriction of general ownership, whilst sticking to their original purpose - to improve marksmanship.

The NRA president testified to congress in 1939: “I have never believed in the general practice of carrying weapons. I do not believe in the general promiscuous toting of guns. I think it should be sharply restricted and only under licenses.”

It was only much later they started lobbying against any and all control.

As interpreted by the Supreme Court in 2008, and affirmed in 2010.