https://www.thehighroad.org/index.php?threads/what-kind-of-guns-do-the-bad-guys-carry.847899/
A couple of (semi)anecdotal findings by the police tech of interest, one being that something like a quarter of guns used in crimes are stolen (more than half are "straw purchases"), the other being that bad guys tend to prefer high-capacity magazines. The latter is hardly a surprise - all things considered, would you prefer a larger gas tank for your car, whether you're driving the kids to soccer practice or running drugs up the interstate?
I'll admit that it's difficult for me to be unbiased about magazine restrictions. Yes, I'm a libertarian and so dislike government regulation more than most, and I experienced the weird grey market of hi-cap mags during the AWB years. But more to the point, every few days I go down to the basement and practice dry-fire for competition, that includes changing magazines as fast as possible. I go to competitions and watch other people swap magazines faster than you can blink. Taking the "battle effectiveness" and libertarian ideology arguments out of it, the "we'll inconvenience a million people in order to maybe save a couple dozen lives because mass-murderers might screw up a reload" argument is just one I have trouble being enthusiastic about, especially when I look around and see the convenience-vs-danger idea not being applied to things like, for example, swimming pools. Surely everyone would be happy to have mandatory breathalyzers built into car ignitions if it saved a couple hundred DUI-related deaths annually, right?