Winchester repearting rifles were popular as of 1870. As they held 16 rounds, could be rapidly fired, and were easily reloaded, there is a strong argument that

Winchester repearting rifles were popular as of 1870. As they held 16 rounds, could be rapidly fired, and were easily reloaded, there is a strong argument that these were, in fact, the first assault rifles. Modern semi-automatic (double-action) revolvers were commonplace as of 1900. Both of the above fired highly lethal ammunition, with rates of fire and reload not that far from modern semi-automatics, which were themselves common by the 1920s. At which time you could mail-order a machine gun to your front door, which is So Not Even Remotely Close To Legal today. Body armor suitable for police wouldn't become commonplace until the 2000s. Ergo, for 130+ years, the police faced a populace armed with high-capacity assault weapons. And for most of that time, they did so with six-shot .38 revolvers and no bulletproof vests. And only in the past twenty-odd years has kicking in doors with guns blazing become, somehow, necessary. So, no, gun ownership, even of high-powered, high-capacity assault weapons, doesn't correlate at all to police violence.