I read a different version of that story. I believe the rifle was the "High Wall" model, his first successful design. Browning and his brothers had made and sold a few in Utah before selling the design to Winchester. Anyhow, Browning convinced the store owner to let him examine the rifle. The store owner reluctantly agreed. After a few minutes of handling, the store owner commented that Browning seemed knowledgeable about the rifle. Browning replied, "I should be, I designed it". Then the store owner snatched away the rifle and showed who he believed to be a smartass kid the door.
That’s the story. I wish I could find that book again, it’s been years since I read it.
I liked the author’s description of the mountain outside Ogden where he test fired everything. The mountain put up with it all until he made the 37mm, then the mountain gave up and large parts started sliding downhill.