The customers can be seen admiring the gun inside a pawn shop while the infant sits on top of the glass counter beside them.
But while they are busy talking to each other, the shop assistant behind the counter leaps forward and tries to grab the baby as it slowly topples head-first towards the ground.
Luckily store manager Bill Reel noticed the child seemed “unsteady” and raced forward to catch it just before it hit the concrete floor.
The younger woman can be seen clutching her hand to her chest in shock as the father-of-four hands the baby to the other woman, believed to be the grandmother.
Mr Reel, who runs Family Pawn in Hurricane, Utah, where the incident happened, said he “just so happened to time it right” and was “pretty shaken up” afterwards.
He told Fox News: “I was scared to death. I grabbed the baby. My heart was racing.
“A four-foot fall going head-first into the concrete, there is no doubt that would have been at least a serious injury, if not some brain injury as well.”
The baby escaped uninjured and the women, said to be embarrassed by what happened, went on to buy the gun, according to Fox.
Mr Reel said he just happened to be in the right place at the right time and urged people to be more careful watching their children and also other people’s children.