So here's my take on this:
I'm not out to stop all crime, or gun crime, or even all 'mass shootings'; I'm interested in dropping the death toll of the ones we see to something 'less' terrible. I think that there's a way to do this while still preserving all aspects of the 2A and the RKBA. Let's be completely honest- people will be able to get guns, regardless of whether they are banned or not, and criminals are still going to shoot innocent people and one another, especially in small-scale crime like Chicago. But those gangsters aren't slaughtering churchfuls of people at a single go.
I'm a strong supporter of proper background checks for all gun transactions, even though I've bought and sold guns FTF before without background checks and I know that checks are limited and no guarantee of future good behavior, I've since rethought that and think we as a community would benefit from universal background checks and hefty penalties if one is caught without those checks. Likewise, I think that every American who can legally possess a firearm ought to be allowed to carry it in a useful condition and manner in all places except those where a firearm poses a clear and obvious danger to the work being done (ie I think that people on trial ought not to be allowed to carry guns into courtrooms, patients in hospitals, chemical plants, etc.) I think that a gun-free zone is a bad idea. Pistols, rifles, etc. I think that we ought to have a national Firearms Permit, issued at no cost to the citizen, signifying that a person is competent and legally eligible to own firearms, regardless of whether or not they choose to. I think that we ought to preempt silly state laws that focus on features or ban carry of weapons and put more guns in the hands of good people, and I think that we ought to develop a functional and useful way to determine who isn't able to have a gun and ensure that they don't (legally) obtain one. I think that guns that are confinscated should be done so with reimbursement at fair market value, and that anyone whose guns are taken from them should have a prompt, speedy and fair opportunity for due process. I'm pretty much of the opinion that guns save lives and ought to be available to every American citizen and legal resident alien. Heck, I'm even open to reinforcing the 2A to clearly and permanently enshrine the RKBA, carry, stand-your-ground, etc in the Constitution.
HOWEVER:
Semi-automatic weapons are more easily employed than manually-actioned firearms; although certain types of action can be run by well-drilled persons at similar rates of fire for some time. This isn't really something that's news to anyone; it's pretty obvious. Now, I think that there is a considerable difference between semi-automatic firearms like the M1911 or a tube-fed 22 or whatnot and combat weapons. Can mayhem be wrought with these weapons? Absolutely, but with some exceptions, it is a lot easier for the average shooter to fire more rounds and kill more people with a modern combat weapon than an older weapon. I very seriously doubt that most people could kill as many people with a Garand in a short length of time than with an AR.
I think that we ought to make "assault weapons" an NFA class, with a hefty-but-not-impossible extra price tag and all of the regulations that it requires. Y'all can have silencers back for that. Full-auto...heck, we can even open the registry for FA, at a rate of some exorbiant tax like $10k per gun. I don't know exactly where to draw the line for what is and isn't an assault weapon; personally, I think that we ought to draw it at 20 round or above magazines and treat each magazine in excess of 20 rounds as an NFA item itself, regardless of what it's connected to (this would let us keep most service pistols and standard-capacity magazines normal and available for carry). So basically, your 20+ round magazines would all be treated as NFA items and unlicensed possession would be a criminal offense. Alternatively, I'm OK with making everything semi-auto with a capacity over 10 rounds an NFA item, regardless of length, action, features, etc. Will this stop mass shootings? No, but it will slow the rate of fire.