You want to pass something that looks like a gun ban, but want it to be as ineffective as possible...
Let's say that you do not know much about guns and don't really want to. You can tell a pistol from a rifle, but the whole nonsense about the difference between a clip and a magazine, or cyclic and sustained rates of fire is knowledge you are never going to need. You are just concerned about murders committed with guns, so you want to ban the sale of things so that this rate will be reduced.
So, you go to the FBI crime stats web page and look some stuff up. You find what sorts of guns are most likely to be used as murder weapons (pistols, rifles, shotguns, etc.) and the circumstances of the most likely murders (armed robbery, domestic dispute, etc.) and figure out the characteristic of a gun most likely to facilitate that murder.
Then for your proposed ban, you pick the opposite.
The least likely type of firearm to be used in a murder in the United States is a rifle.
The least likely type of murder in the United States is a mass murder.
Given that, a gun ban almost guaranteed to save the fewest number of lives would be a ban on a subset of rifles (assault rifles) and the gun feature most useful in a mass shooting (a high-capacity magazine).
Now, I'm a gun supporter, but I recognize that there are other views and I support the right of those people to try and get those views into public discourse and policy (even if they do not support my right to do so). If you are one of those people with a different view and a gun or gun-feature ban is part of how you want to drop the firearm homicide rate, at least do it right and propose and support bans on something that will make a difference.
If every rifle in the United States were to vanish and never be replaced, and every mass shooting were to stop for lack of high-capacity magazines, the difference in the firearm homicide rate would be less than the difference that happened all by itself from 2010 to 2011.
Maybe you are going for the assault rifle and magazine ban because it has just been hyped on the news, or because it is particularly low-hanging fruit or because you are just looking for something symbolic or a getting foot in the door for some other legislation years down the road. But if you are actually trying to reduce firearm homicides and think that right now is the best (or possibly only) chance in the next several years to get a substantive ban on certain weapons or features passed...then try for something substantive.
I'll continue to disagree with you, but at least you will be working towards something whose effects will be distinguishable from the statistical noise.