NapoleonXIV said:
Precisely, thank you, also please peruse again the original scenario I proposed.
The breakup would start when most criminals had tommyguns, and gangs started to equip themselves with BAR, M1919 machine guns etc. Police would very quickly demand the same, armored vehicles and light artillery. Gangs would respond in kind.
Gun manufacturers, responding to public rather than military demand, would supply this market with smaller and smaller weapons, evolving very quickly towards something like the most modern assault rifles. These would be very light and effectively usable even by children.
The bazooka, giving gangs and individuals the equivalent of heavy artillery, would accelerate the process, again, gun manufacturers and public demand would speed up the development of such extensively over OTL. Grenade launchers and shoulder fired missiles would become de rigueur in a very short time. At this point or before the police would quit in favor of the military. Once that happens the breakup is inevitable.
This is a worst case scenario and it does require that absolutely no gun control be established before the breakup goes to full development and there is no US. (perhaps there is a Constitutional provision which very clearly prohibits ANY gun control)
That's the result if there's absolutely no gun control, but in reality, some measures would be taken before it got that bad. Without Prohibition, you don't see real pressure to restrict weaponry until the 1970s, and not really until the 1980s.
Obviously no one's going to be selling bazookas or heavy weaponry on the open market. It simply isn't economical. The only private individuals who would be interested in purchasing a functioning artillery piece would be the ones you wouldn't want to have one. And their numbers are far too small to create a market, anyway.
You might see the beginnings of gun control in the early '70s, as the antiwar groups that grew during the Vietnam War lose their moderate members, who see the mission as accomplished, as in OTL. With cheap automatic weapons making their way to the US, and into the hands of these groups, you'll see both sides of the aisle voting to prohibit the importation of fully-automatic foreign firearms.
It's a step in the right direction for those who want to prevent gun violence, and American gun manufacturers will be pleased, since it allows them to sell more merchandise. As you get the urban decay of the 1980s, and see more gang violence, you'll probably see further restrictions in the weapons available to the public. These laws will probably stay in effect until the mid-'90s, when they'll be rolled back.
The major effect of this is that automatic weapons can still be purchased by the general public until 1985, and that there are far more on the open market.