CR for the U.S. ca 1921

[HANS]

There are several points to this.

1. The things were pretty much legal for most of the 1920s and in most of the US.
2. That doesn't mean they were common -- far from it. They were very expensive and difficult to find (usually you have to order from the manufacturer or steal from the police). That's already a good reason for investigators not to have them.
3. However, you might want to examine your reasons WHY you don't want your investigators to run around with them. If you're just following the misguided "feel" of Call of Cthulhu, which terms gunfights stupid and, essentially, bad roleplaying, think again -- if you were someone investigating something dreadfully horrifying. Wouldn't you equip yourself as best as you could, like any sane man? Remember, some of HP Lovecraft's characters even armed up with flamethrowers and regularly used dynamite etc. The key is to ensure that the submachine guns can't beat the horror.

Cheers

HANS