I think there is also a huge x-ray machine on entry into the USA (big yellow pillars).
Whenever we have a firearm with us, we're asked whether we have a firearm. If we don't have a firearm with us, we're not asked. One crossing we hade two firearms and a border agent was walking around the back of fifth wheel and up the passenger side with his hand on his weapon before the other agent even asked us about them.
Just crossed this past weekend, no questions about firearms either way. Was asked about knives at the Canadian border crossing but not guns.
The Canadian agent told me she was still waiting for the data to show on her screen, based on the licence plate number taken from the camera. I handed her the list of my purchases and she kept waiting for the computer. I've known her for years, but she still waited until the data came up to clear me through.