This number is a little bogus. The NRA will endorse any sure winner just to pad this statistic. In some cases, they've endorsed blatant anti-gun rights candidates because they were "sure he could win." I don't think that the NRA is any more a shill for the Republican Party than the GOA is for the Libertarian Party, but neither organization makes me particularly proud.
Otherwise, it's good to hear that the anti-gun rights movement is having trouble getting traction.