Of course restricting magazines and accessories is not effective. They're only brought into the argument by people who don't want effective gun control.
But restricting guns and ammo is absolutely effective. The UK has a sixtieth of the rate of gun deaths compared to the US. And the UK is no paragon. Its rate is much higher than it should be, in my view, because a lot of gun crime is gang related so does not get the attention it deserves. A more reasonable rate would be closer to Japan's which is about a quarter of the UK's. Much lower and you likely start requiring genuinely authoritarian regimes such as Singapore or HK.
The US could absolutely get to saner gun crime and homicide levels if there was any real will to do so but there isn't. Of course it wouldn't happen overnight but it doesn't have to.
The real problem, in my opinion, is that the US is so de-sensitised to extreme violence that they can never have the equivalent of the collective traumatisation that the UK had after Dunblane. That was the spur we needed to put rational gun laws in place. The balance in the US is so far out of kilter that the seesaw is buried in concrete. Even biblical massacres of innocents can't shift it. So very very sad.