History (long)
Here is some history. The first major use of full auto weapons in crime occurred in the days of Prohibition, when the sale and use of alcoholic beverages was banned by a constitutional amendment and its enabling legislation, the Volstead Act. Naturally, as with the ban on narcotics, criminals were willing to supply something that people wanted but which was illegal. And again naturally, they fought over territory, using that new invention, the Thompson submachine gun. There was a lot of agitation for controls or a ban on such weapons, but no federal law was passed until several "massacres" occurred, using "Tommy" guns. (The St. Valentine's Day Massacre in Chicago being the most famous, but not the only one.)
When the Depression came on, many people who had previously been small time crooks or trouble makers went big time, often with the tacit support of their families and other "common folk" who had lost everything and were happy to see the big banks take a loss. Automatic weapons thus became a favorite of "independent" criminals like Bonny and Clyde, "Machinegun" Kelly, and others.
Franklin Roosevelt was elected on his promise to end the Depression. It is often alleged, correctly, that FDR did not end the Depression - that honor went to Adolf Hitler. But Roosevelt considered crime one of the "social problems" he wanted solved. One step was to push through a repeal of Prohibition, perhaps not co-incidentally enriching an old supporter who had brought a small ocean of whiskey into the country "in bond" until it was legal to sell it. Thus was the Kennedy family fortune made. (Joe Kennedy was not a "bootlegger" or seller of illegal liquor; he was smart enough to get the liquor positioned until the time was ripe. When other importers tried to sign deals with Scottish distilleries after repeal, they found that Kennedy had tied up the supply for several years.)
Roosevelt appointed as his Attorney General a man named Homer S. Cummings, a humorless, straight-laced and fanatical former prosecutor, who determined to ban all privately owned guns in the U.S. Told that the federal government did not have that power, he decided to use the government's taxing power. The bill he sent to Congress required registration of all guns, and imposed prohibitory transfer taxes on all guns and ammunition. I am not sure of the exact numbers, but I think it was $2000 on a machinegun, $1000 on a handgun, $500 on a rifle, and $200 on a shotgun. Centerfire ammunition was taxed at $10 a round, shotgun shells at $5 a round, and rimfire ammunition at $1 a round. Congress finally did pass a law, the National Firearms Act of 1934, but eliminated all the taxes except the transfer tax of $200 on machineguns and some other "gangster weapons", including silencers, so-called. (For today's equivalents multiply by $40, so a box of .22 cartridges would have been taxed at the equivalent of $2000. A shotgun would have been taxed at the equivalent of $8000 and each shell at $200.)
The NFA seemed to work as crime did drop off (mainly because the sale of liquor was now legal), and the Roosevelt administration decided to try again to control other firearms. The result was the Federal Firearms Act of 1938, which established the licensing of dealers, and much of the rest of the current federal gun laws. That use of the taxing power, thought up by Cummings, was the reason that until recently, the enforcement of federal gun laws was done by the Treasury Department, as tax evasion is the actual crime under those laws. (If a person buys and sells guns without a license, say, or owns an illegal machinegun, he is evading taxes.)
Few today realize how close FDR came to his dream of a total gun ban, and how close he came to realizing his other dream of becoming an American dictator. While he was not in the league with Hitler or a posturing buffoon like Mussolini, there is little doubt that he would have been willing to establish concentration camps for opponents, as he did for Japanese and Japanese-Americans later. Had the war not occurred to give him bigger problems than worrying about armed Americans, who knows what he would have done to destroy our freedoms?
Jim