Update: When I originally blogged this, I was unsure about the terms "NRA" and "NRA-PVF". I contacted Lorien Johnson, NRA's Campaign Field Representative in St. Louis, to clarify the ratings of both Brad Lager and Peter Kinder. She wrote back:
NRA and NRA-PVF are under the same umbrella of NRA. PVF is the Political Victory Fund, the arm which makes endorsements, sets rankings, etc.
Kinder and Lager both earned an A+ ranking. Kinder received the endorsement.