Even then his argument isn't valid. How could Dom know at a glance what type of revolver? Was Dom an expert on revolvers? Did Dom say it was a different type of revolver? Dom had just witnessed a policeman being murdered in front of him. I doubt he was really that concerned if it was a Smith&Wesson.
You're correct... and no, Benavides did not attempt to state the make and model used by the killer.
However, Walt believes that the weapon was not a .38 Special Smith & Wesson (like Oswald's was) based on the eyewitness testimony describing the manner in which the killer ejected the shells.
Walt is wrong, of course, but that is the argument he has made in the recent past.