It really is an NRA lobbying and PR thing. Prior to Wayne LaPierre's elevation to leadership in the mid-70's, the NRA was largely an apolitical sport/hunting group. They weren't pushing for the right to have military weapons or the right to open and concealed carry like they do today. They weren't pushing the interpretation of the 2nd Amendment as being an absolute right for anyone to own anything, nor was anyone else, really. Since then, they've been pushing those things non-stop, spending tons of money on lobbying, "education" and PR and doomsday appeals to members that the big bad left wanted to take ALL their guns away and take away their ability to PROTECT THEIR FAMILIES because, you know everybody's household is under siege by evil strangers with guns. Now it's almost accepted by everyone that the 2nd Amendment has no limitations, helped partly by some supreme court rulings that didn't go quite that far but helped their cause (you still can't legally own SAM's and the like, though nobody ever talks about the big stuff as being part of the arms referred to in the 2nd).