American reddit readers I would like to know if there are 5 million NRA members and 350 Americans in the USofA why is the NRA so powerful?

I understand your 2nd amendment allows you to keep and bear arms - nothing about ammo and nothing to me that indicates there are no conditions to gun ownership like registration. I have also heard you can take the second amendments away from criminals, and others as well - help us non-Americans understand. Thanks

Edit should read 350 million Americans