NRA membership levels amount to about 2% of the adults in the U.S. 2% of the country is not enough to force Congress to comply if the other 98% don't agree.
No, its not enough if the other 98% disagree, but first off, the other 98% would have trouble agreeing that the sun rises in the east and sets in the west.
The other thing, and the one the numbers alone don't show, is the real reason the NRA is so respected/feared. Those who AGREE with NRA members and VOTE, but aren't NRA members.
A Silent majority kind of thing. Politicians know that its not JUST the NRA members, but their families, friends and others who aren't on the NRA's member lists but hold similar opinions about the issues, and do vote, that give the NRA its political clout.
PLUS its the tendency of firearms enthusiasts to make the gun issue THEIR issue, and vote against gun control politicians, even when they agree with them on other issues.
So, belong to as many pro gun groups as you want, just remember that while you may disagree on tactics, we are all on the same side.