Five reasons the NRA wins
An insightful article by Amy Showalter. She notes the conventional media narrative is "NRA has lots of political money with which to scare politicians," but that's not the key. Keys are things like armies of well-informed volunteers, face to face contact, old-fashioned personal persuasion.
There may be a deeper issue here. NRA has members, Brady Campaign has customers, you might say. They have no voice in the organization, or its policies or leadership. It puts products (bills, messages, and (when it can get any) legislative successes) to them, and they send in contributions.