A) 4.2 million members in a country of 315 million means a core policy of this country is controlled by-at most-1.3% of the voters (that's assuming all NRA members are eligible voters, vote and vote the NRA party line).
B) I wonder how much of the boost of the NRA membership is due to things like their recent campaigns essentially making membership free, like this one:
http://forums.anandtech.com/showthread.php?t=2293393
C) Interesting factual analysis on the Rachel Maddow show a few nights ago. She analyzed the effectiveness of various right wing lobby groups during the 2012 election. The group with the worst record of all was the NRA with less than one percent return on their investment (0.89% IIRC), meaning that the NRA spent its funds on the winning side of a race less than one percent of the time.
I think this country has had a sea change in public opinion about uncontrolled and unfettered distribution of military style weapons. The NRA is about to be left in the dust (assuming the public can force Bohner to allow any bill to come to a vote).