Money on money as an epiphenomenon:

“…a closer look at the background check vote — and NRA influence generally — reveals that there’s more at play than just cash. A lot more. The backgrounds and histories of the two sponsors of the background check amendment — Joe Manchin, a West Virginia Democrat and Pat Toomey, a Pennsylvania Republican — illustrate some of those complexities.

Both Manchin and Toomey have “A” ratings from the NRA — or at least they did until last month. Both represent states with large numbers of gun owners. Pennsylvania has more NRA members than any other state, and sells more hunting licenses each year (2.5 million in 2012) than any state except Wisconsin. And Toomey has been the Senate’s leading beneficiary of NRA largesse. In 2010 the NRA spent more than $1.79 million to elect him and an additional $1.15 million on negative advertising to defeat his Democratic opponent Joe Sestak Jr. Thanks in part to those court decisions that loosened campaign finance limits, the nearly $3 million the NRA spent on the Toomey race was more than three times the total amount spent by the NRA for all of Toomey’s Senate colleagues combined between 2000 and 2010.

Asked about its spending on Toomey — the most the NRA has ever spent on any candidate — NRA President Keene joked, “It just shows what money can do for you.” The reality, however, as Keene acknowledged, is that the NRA’s spending on that particular race — in which Toomey spent a total of $17 million against his opponent’s $12 million — may have very well made a critical difference. Toomey won by only two percent of the vote.
publicintegrity.org

It looks like the NRA’s position is that we shouldn’t be paying attention to what they spend.