I look at it a bit differently. I want politicians hands tied, not because "we can't possibly stop it" but because what they want to do WON"T stop it, and will only increase the cost and burden on law abiding people, and in particular those who enjoy firearms as a hobby.
If he accepts the argument that harm can be done with smaller capacity magazines, "so why not ban the hi-caps", the other side of that coin is "Why BOTHER to ban the hi-caps?"
Perhaps he believes that while responsible people can have matches, no one should have a butane lighter, because somewhere out there is an arsonist in waiting?
At the risk of sounding too mystical (or perhaps too nerdish), your brother simply does not understand the "Riddle of Steel"
The blade is nothing without the hand to wield it.
What I object to about the gun control point of view is their obsessive focus on this or that TOOL, and apparent lack of interest in controlling the "hand". And I'm not talking about who's hand a gun may be in, but what the hand with the gun does.
Considering we have had laws against killing people for fun or profit, from the beginning of laws, and they have not ended the killing.
Its the hypocrisy that upsets me, they claim it will end the violence, and they know it will not. Banning this or that tool can only, at best, shift those so inclined to another tool. I would have you remind him that no guns were used to kill all those people on 9/11/01.
And so called "safe storage" laws are not the answer, either. Several of the killers in the recent past have either stolen the guns, or killed the owners and stolen the guns. And that includes having to break into a gun safe to get them. Such laws are only excuses for govt. agents to be in your home, doing inspections, and a justification for the govt to reach into your wallet (fines) if you fail to comply with their arbitrary rules.
Consider the extremes to which these people go...recently the Mass govt had a choice to make. They either had to put trigger locks on a pair of displayed muskets (originals from Lexington and Concord), or remove them from display, because children were allowed in the building! Otherwise, they would be in violation of current Mass law. Nearly 5 foot long muzzle loading flintlocks, some of the actual guns used firing the opening shots of our Revolution, yet they were not "safe" to display where children could see them, UNLESS they had a trigger lock installed.
Gun=bad, evil, dangerous, that all they see. That's all some will see. Anything and everything, rational or not, is grist for their mill, in pursuit of their vision of a "better world". And that includes the blood of innocents.