Obviously gun control would make a small impact on people 'losing their heads' for 2 mins as camel put it. However i can't see it stopping any of these spree shootings which are almost always planned over the course of weeks. I also fear it would mean normal law abiding citizens would go about buying weapons illegally thus providing a new market to organised crime.
In the same way i think it would be hard for us to ban cigarettes or fish and chips
Growing up (I'm not yet forty) shotguns were left laying around my grandparents house - gun safety was considered to ensure shotguns were propped up in the corner of a room and cartridges in a bowl on the sideboard or in a belt on a door handle.
Me and my cousins were always playing army, etc with them (unloaded - we weren't quite that daft).
My dad was a little more sensible, his guns were kept in a wardrobe with the cartridges on a high shelf but again I used to get them out when I home alone.
Had I flipped one day, or if we had been burgled, there could easily have been some damage (though I suspect a lot less with a couple of shotguns than the USA has recently seen with pistols and automatic weapons).
When the UK controls kept getting stricker and the licence fees went up and up eventually my Dad couldn't be bothered with the hassle or expense and got rid of them.
Gun control would have a massive impact short, medium and long term.
Short term the majority of law abiding people would hand over their guns as they did in the UK when handguns were banned. If there is any kind of register you can't simply lose the guns.
Medium term to long term the supply of guns would reduce further as guns illegal guns are gradually discovered by the police and the supply of legal guns reduces as gun manufacturers close down due to lack of sales.
Some criminal's will always get access to guns but basic economics dictate that reducing the supply will drive up the price and drive down the demand. The average UK criminal doesn't carry a gun as they are hard to get hold off, incur serious jail sentences and are not needed as you are unlikely to be involved in a shoot out with the police or general public.