Been too pained with rattlesnake bite to do much writing, but while out of town I researched the papers of Homer Cummings, Attorney General in the 1930s. Found an interesting 1935 memo to him from J. Edgar Hoover (who then signed his name John Edgar Hoover). Hoover is shocked that they have invented the .357 magnum. He adds as a secret tip (apparently they had informants in Smith and Wesson) that the company intends to bring out ... jacketed bullets for it.
He says that the only purpose of such a round is to penetrate body armor, since we all know that stopping power isn't helped by high velocity bullets, but by heavy slow ones.
He also worries about zinc bullets (I know this was explored in the 1980s, didn't know the idea was then half a century old). SInce zinc is less dense than lead, but much harder, these cast bullets could be pushed at much higher velocities and thus might also pierce body armor.
There are also AG memos on how to push more gun control. The tools are pretty much what they were decades later. Send press releases to all newspaper editors. Get radio interviews. Rope in the League of Women Voters and the International Assn of Chiefs of Police. Appeal to labor unions by tipping them off that big corporations own full autos and tear gas guns, presumably for use against strikers.
The big push was to be for national handgun registration. The original form of the NFA 1934 had taxed and thus registered not only full autos and short barrels, but also pistols. Congress took pistols out, and Cummings' people had drafted another bill to put pistols back in.