It is debatable how much of the drop in crime is attributable to the gun ban, given that the USA had a larger reduction in firearm crimes during the same 20 year period than either Australia or UK did. Certainly, we're higher than them now, and were higher than them before, but the gun bans contribution to the lowering over the last 20-25 years is hard to gauge given the larger reduction without a ban.
The more salient part of course being the violent crime rates, rather than simple gun crime, but that gets into so many different ways of tracking things that it's hard to judge.