Most firearms of all kinds are already widely available in the United States. No doubt any criminal can choose the gun to his liking but I don't consider this a weighty argument for making gun even more accessible.
The FBI concluded that criminals with 'grade up' if their preferred weapon is not available. That is, they will tend to choose a weapon which is more lethal rather than less.
They also concluded that criminal require weapons for protection against their own peers so going without is a non-option no matter what the law says...and as a reminder to the not-so-bright, these people are classified as 'criminals' because of their interaction with laws. This self-protection against their own is one of their primary incentive for carrying weapons while using them for criminal endeavors tends to be more secondary.
When confronted with these facts most 'progressives' will probably argue that if guns were made illegal then criminals will drop their criminal ways and go to med school. Especially if it's free. My belief is that most 2018 vintage progressives are border-line retarded. Particularly when it comes to system analysis.
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In real life, a few weeks ago a neighbor of mine who's husband died a few years ago was burglarized while she was away on travel. A sharp-eyed neighbor saw the criminals leaving her driveway, investigate, and called the cops. The perps were caught after a car and foot chase.
The perps were meth heads as is usual for my area. They made the mistake of stealing a few guns. Had they not, they would have spend a few weeks in the county jail. Since the crime did involve guns, they will be going to the federally operated big-house for some number of years.
I point this out because the FBI report I mentioned suggested increasing penalties for gun related crimes. Very common-sense and it has worked; gun related crimes plateaued after this action was put into place a few decades ago and have been declining ever since. Basically criminals are pretty aware of how the law works and take pains to avoid performing crimes with or relating to guns. People who constantly say 'we need laws' don't know their asses from their elbows. We've got plenty of laws, and they work remarkably well.