Nah, you ban "assault rifles" and they just use semi-automatic rifles that don't fall under the "assault-rifle" category.
So you ban all semi-auto rifles and they use semi-auto handguns.
You ban those and they use revolvers with speed loaders.
I mean there's a long way to go until guns are no longer the preferred method of conducting these kinds of attacks.
But really, you ban one type/style and you still have people who have them that are completely unknown. These guns can remain operational for hundreds of years if even kind of cared for.