Actually they give alot more, its not just individual contributions.
NRA Contributions: How Much Politicians Like Roy Blunt Receive | Fortune
Fortune is not a liberal mag.
Also the nra is owned by the gun industry, which why most of their members are for greater background checks but they arent backing that because they arent doing their members will, its the gun industries will.
Here is the break out of how it works
This Is How The Gun Industry Funds The NRA - Business Insider