This is interesting but I suspect they are low.
I’ve seen the ~270 million estimate before, but from what I can discover it is almost entirely based on ownership surveys. I’ve been around gun owners all my life. They are honest people to a fault. They are good natures, open, and cooperative in all things. They also have some serious misgivings about their governments motives and use of gun registration and survey information. Especially those born before the New Deal.
If they admit in a government survey that there are 270 million guns in the U.S. then I would lay odds that there are many more than that. In the south, I would lay odds that there are that many in hand while the census boys are around.