Not sure if you're joking there -- maybe you meant magazines?

Like so many other gun regulation ideas, it seems superficially reasonable based on "danger" but it's almost never the case that items like that contributed measurably to gun deaths. They don't need to be banned -- they are niche items. Mass shooters who have access to them rarely use them. They rarely use 40 or 50 round magazines. Indeed, people rarely purchase magazines larger than the standard 30 rounds.

We can reduce gun ownership...

That is not a legitimate policy goal. The earlier poster points out that gun ownership is not correlated with crime at all. We shouldn't set policy goals that are merely about partisanship -- trying to cut down on gun owners because we don't like them -- rather than a clear public benefit.

...increasing liability for dealers.

I would like to better understand what you have in mind here. In general, modern legal systems reject holding one person responsible for the crime of another. If a mass shooter lawfully purchases a firearm, what possible liability could a dealer have?