In my opinion, the OP handled an awkward situation tactfully. He avoided an argument with the clerk and didn't try to sell the women on his own point of view.
In his shoes, I might have done two more things. The first would be to suggest to the women that, if they hadn't already, they take an introductory handgun class from a disinterested provider, preferably one aimed at women. The second would be to send a letter to the store manager which listed all the clerk's misinformation and suggested that, in the interest of not alienating potential repeat customers, he train or screen his sales staff better.
In his shoes, I might have done two more things. The first would be to suggest to the women that, if they hadn't already, they take an introductory handgun class from a disinterested provider, preferably one aimed at women. The second would be to send a letter to the store manager which listed all the clerk's misinformation and suggested that, in the interest of not alienating potential repeat customers, he train or screen his sales staff better.