The gangbanger on the other hand would be calm and collected having experienced armed conflict before.
I investigated gangs for well over a decade and was involved in numerous arrests and interviews of gang members during that time, many of whom had been involved in shootings. We're not talking combat veterans here. Many of them, especially the ones who had been shot before, or had seen their buddies killed or turned into paraplegics were not real happy about being on the wrong end of the gun. Sure, there some cold, hard individuals out there, but the idea that you have all these street-combat hardened veterans out there is pretty much bunk, in my experience.
Robbers usually get off on the power aspect inherent in the crime, but they are looking for easy money and don't want to get shot. Often, there's some type of wind-up for the crime where the victim gets a bad feeling about the situation before he is approached. At this point, before things really take off, the sight of a gun in the victim's hand, maybe just held at the side pointed at the ground, might be enough to derail things and send them off looking for another victim. Just my 2cents.