The support for McCain's conservative credentials came as former U.S. Rep. J.D. Hayworth traveled the state telling Republicans that McCain can't be trusted to support issues important to them.
Hayworth has attacked McCain's record on gun rights, saying the incumbent has supported restrictive legislation, including a measure to close the so-called "gun-show loophole" that allows private sales of weapons without background checks.
The NRA, however, said McCain's overall record is friendly to gun owners, despite past disagreements.
"You have demonstrated a proven commitment to our Second Amendment rights," NRA Political Victory Fund Chairman Chris W. Cox wrote to McCain.
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The letter cites McCain's opposition to bans on assault weapons and handguns in the District of Columbia, as well as his support for a law prohibiting lawsuits against gun manufacturers when their weapons are used in crimes.
Hayworth countered with an endorsement of his own Thursday from former NRA president Bob Corbin, who also served as Arizona attorney general.
"For 12 years while he was in Congress, J.D. maintained a perfect ‘A' rating from both the NRA and the Gun Owners of America," Corbin said in a statement released by Hayworth's campaign. Read more.