I'll admit it was an exaggeration to imply that the copious number of pawn shops was due to stolen goods being actively fenced through the shops-
And there it is.
Nnobby45, when number of bad guys = N, and number of rounds = N-1, it's not a good start.
It might have been enough to scare them off. That is speculation.
If it hadn't scared them off, it would have offered too few rounds. That isn't speculation.
You are certainly right in that not having enough ammo for the number of bad guys isn't a good way to start off a confrontation and that if having a gun would have been enough is speculation. However, it is that speculation that is promoted extensively by those citing Kleck's 2.5 million defensive uses of guns each year, more than 6800 times a day. After all, it is only in a small percentage of those 2.5 million purported events that guns are fired in self defense.
However, this is one of those cases where simply being present was enough to drive the criminals away. Of course if Nicholas had been armed with a gun, I am sure the gun would have been noted as the reason for the robbers taking flight, but that wasn't the case here at all. As noted in the OP, we don't know how many of the six criminals Nicholas actually encountered, but as Nicholas' father noted, they appear to have been startled by Nicholas and retreating at the time of the shooting and did not remain after the shooting.
Whether a 5 shot revolver would have been enough if it didn't scare them off is also speculative. As noted in the OP, we don't know how many bad guys actually were in the house during the event. Six were arrested, but that doesn't mean six were in the house or that six were encountered by Jackson.
With that said, the robbers were driven away by their encounter with Jackson and he wasn't armed. They did all the shooting.