That's a ridiculous thing to say.
The UK introduced gun control in the 1990s to deal with the Dunblaine Massacre at a primary school. The actual law didn't have much impact at all because most people didn't have guns in the first place. It probably helped to reduce gun crime in the future.
What you're looking for is "gun control implemented on this date, gun murders dropped radically after this date" to prove that gun control works. Which ignores almost all of the reality of what that gun control was, and what the gun control was before this.
You also seem to have an attitude that if gun murders go up or down without there having been a piece of legislation to make it so, that gun control doesn't work.
The problem is there are various things that can lead to higher or lower fluctuations of gun murders. A gun law implemented doesn't mean that there will be a specific number of murders in a year. That's ridiculous.
For example in the UK there was a problem with gun violence in the early 2000s, and they didn't need more gun control to try and deal with the problem. The gun laws in place helped the police to deal with the problem, hence why gun murders went down.
A law doesn't do anything. You can make all the laws you like, if no one is A) enforcing them and B) being proactive in dealing with crime in the first place, then there's no point.
You say that the places with the highest murder rates are the places with the strictest gun control. That's complete bullshit. The fact that you haven't actually backed up your claim is telling, because I bet you have no idea what the statistics actually are. You just made it up hoping that I'm a stupid idiot who'll accept your bullshit.
List of U.S. states by homicide rate - Wikipedia
Here are the statistics.
Number one is Louisiana with a murder rate of 10.3
Louisiana is not a liberal state, it has the highest prison population IN THE WORLD. It has lax gun laws, it has a murder rate double most of the USA including, ironically, California which you claimed has the highest murder. (Probably because you're looking at number of murders rather than murder rate which is really amateur)
How Many Gun Owners Live in Your Home State?
Here are the state rankings for murders, and their ranking for the percentage of owners of guns.
1. Louisiana - 13th
2. Mississippi - 6th
3. Missouri - 21st
4. South Carolina - 18th
5. Maryland - 42nd
Now, the top four also have a high percentage of gun owners. Maryland is different, but then I'm going to bet that a lot of guns are in the hands of people who shouldn't have them, but get them because it's easy to get illegal guns.
Gun control is worthless.
Well, tell that to the 2,977 British people who don't die EVERY YEAR because of gun control.