Economists probe question of NRA electoral power
Dave Kopel has a study by Christopher B. Kenny, Michael McBurnett & David J. Bordua, on the question of how much NRA endorsements influence elections. (pdf file) Among other findings:
In 1994, each 10,000 NRA members in a district was associated with a 5% vote gain for the candidate NRA endorsed.
Challengers benefitted more from an endorsement than did incumbents.
An endorsement helped a Republican contender more than it helped a Democratic one.