Our murder rate was much worse when people were still using revolvers.
Any chart ever made of US per capita murder rates. Back around the time of Constitutional ratification, when everyone had to murder with flint-lock muzzle loading pistols, the US homicide rate was about 28 per 100,000. The Colt revolver got that down to about 8 to 12. Switching from revolvers to high-capacity semi-automatics dropped it down to about 5.
The European homicide rate prior to the wide adoption of the flintlock usually ran somewhere between 20 to 100 per 100,000.
Homicide trends in America: 1850-1950
from Carnegie Mellon.
Long term trends in US homicide rates
Long term trends in violent crime
, going back to the 1300's.
Of course, perhaps I'm trying to trick people into reading really interesting studies of violent crime trends throughout history. It's a place where a dedicated researcher can actually produce a lot of data because crime has always generated a lot of public records.