I think we’re spending more time talking about who is / isn’t part of the problem / solution than we are at addressing the OP, so I’ll just copy/paste most of my recent specific thought in the slightly more controlled thread on min-maxing gun laws that has been repeatedly mentioned in thread.
So, while it has a bad reputation in gun-owner circles, I think that in conjunction with a 10 round magazine cap, variants of the bullet button legislation could be a workable improvement to our federal laws. I find this as something as a compromise between those who want smaller maximum capacity (say 5 rounds) and those who want a larger capacity but also want to take effort to slow / impede the possibility of fast magazine changes that certainly aid mass shootings.
For those not familiar with the concept, CA’s original legislation, since changed, required semi-auto firearms sold in state to not have a single push button magazine release, but to instead have it recessed sufficiently to require some sort of tool (at one point even a bullet tip qualified) to release the magazine, before another could be loaded. Not surprisingly, tons of work arounds were quickly released to the market and lots of lawsuits and counter legislation followed.
But in theory, especially if well written and federal (so that it isn’t a sub set of guns, but all guns on a national level were involved) you could get a large improvement in slowing down mass shooters, while preserving a slightly larger individual capacity, a compromise that might appeal to a wider group.
(and yes, I fully acknowledge that there would be people who in a heartbeat who illegally modify these weapons given a chance, but at least it’s at least another 1-2 stages where they could get identified beforehand)