No. That's a rumor, like replacing the glove against Cooper. Liston smacked Ali in the face and threatened him, and Ali left. Nobody carries a gun with "blanks" in it. Not now, not then. Certainly not security guards in casinos.
Caught on camera for a film adaptation. It was just a tacky addition to sensationalize the events leading up to Ali's first title-winning performance.
Although this was staged, he did look different in color. https://www.youtube.com/watch?v=IzGqvIspmRM His arms were made for boxing.
It had to be a theatrical gun that shot caps. Blanks shoot a compression wad that can injure from a few feet away.
No, the story that he pulled a gun is just a tale that came from that 1970s book and film that purported to be Ali's autobiography. People who were actually there said Liston either smacked Clay or got close to him, said something, and scared him off. Liston was a practical joker and probably did, at some time, have a toy gun and exploding cigars etc. But I doubt he would be pulling a gun in a casino, and certainly not carrying a fake one there.
It is a widely believed fact that Sonny Liston killed Cassius Clay in 1964. Clay was replaced by a look alike named Muhammad Ali.