My experience has been...
In the 70's and early 80's... mostly cheap saturday night specials. Pot metal guns like the Raven, Davis, Jennings, RG. Probably the most popular Col. being .25. But al hofge-podge of different calibers, mostly .25's, 32's, .38's, an occasional .45.
It seems that in the late 80's bad guys started taking guns seriously. I started seeing better quality revolvers and autoloaders. In high calibers like .38spl, .357, 9mm, and .45
In the late 80's and into the present the 9MM became the gun to have. Probably because of violent rap music. Yeah I said it. Also started to see military style rifles. Firearms becoming fashion statements, and status symbols. As they increased firepower they seem to have increased there willingnes ro use that firepower for little or no reason.
Once I participated in a search for a shooter. (killed an innocent bystander) We raided his mothers house where he lived. He wasnt there but two things struck me as unique... One was this guy had about 200 pairs of sneakers. The other that he had stacks of popular gun magazines. Scary...