If I ran for Senate, I would vote against most gun regulations. It wouldn't matter if the NRA donated or not.
Is it possible, that the cause and effect have been reverse here? Perhaps the NRA gives them money because the candidate already believes the 2nd Amendment must be protected and they obviously want that type of person elected.
It's the same thing with Unions and Democrats. Unions aren't buying their vote, they're helping to put them in office because they already believe unions are a good thing.