OK
First, let me say that I have no interest in punishing lawful gun owners. Second, I don't feel that there is any legislation that could be passed that would prevent a nutter like Adam Lanza from shooting up a school.
So, IMO, there should be a mandatory screening process any time a person buys/acquires/takes possession of a gun. No exceptions. Criteria needs to be set in place as to who is, and who isn't allowed to own a firearm (ie someone convicted of a violent felony). There should also be mandatory training involved if you wish to carry your gun, with mandatory classes to be taken every year or so. If people want to carry in public, they should be able to show some proficiency in the use of that gun, and an understanding of the laws. There should also be a registration process for all firearms. I understand the slippery slope involved in this, but the goal here should be to weed out the criminals, not punish the law abiding gun owners. Sentences should be EXTREMELY stiff for anyone caught with a gun that does not belong to them. Straight to prison, minimum mandatory 5 year sentence just for possession of the gun. This to me is where legislation could have the biggest positive impact. Perhaps a young kid will think twice about carrying around a stolen gun if he knows the severity of the penalty.
Outside of that, I don't see much else that would be effective. Limiting the types of guns, and the capacity of the magazines is a bit trivial, imo. I personally don't see the need for a citizen to own an automatic weapon with a 100 round clip, but if the person is a law abiding gun owner, then I feel his/her right to own said weapons outweighs the potential societal benefit of any laws limiting the types of guns he/she could own.
in counterpoint, the second amendment of the constitution was drafted to enshrine that Right specifically and to preserve it against encroachment by any future do-gooder or despot who might try to disarm the populace.
the second amendment was not created in a vacuum, but with a long history of disarmament leading to despotism.
when the Scottish Parliament signed the Act of Union in 1707 it was followed by several uprisings. these Jacobite rebellions resulted in the Disarmament Act of 1747, which made posessing any weapon (even knives) a criminal act. shortly thereafter, scotland was subjected to "The Highland Clearances" which would today be described as "Ethnic Cleansing" where poor folks were driven off their farms, and into "labour villages" where they were allowed to choose either slave wages harvesting kelp or starvation.
in 1776, the founders well knew the price paid by the nwo helpless scots highlanders for defending their freedom, and took steps to ensure such a thing could not happen in their new nations.
the right to Keep (own) and bear (possess on your person) arms (weapons of ANY description) were crafted carefully with a justification clause, so future generations would know WHY it was there, and absolutely unambiguous language regarding what infringements were permitted (NONE).
even the case of US v Miller touted as proving the constitutionality of gun bans says nothing of the sort.
"In the absence of any evidence tending to show that possession or use of a "shotgun having a barrel of less than eighteen inches in length" at this time has some reasonable relationship to the preservation or efficiency of a well regulated militia, we cannot say that the Second Amendment guarantees the right to keep and bear such an instrument. Certainly it is not within judicial notice that this weapon is any part of the ordinary military equipment, or that its use could contribute to the common defense. Aymette v. State, 2 Humphreys (Tenn.) 154, 158." ~
http://www.law.cornell.edu/supct/html/historics/USSC_CR_0307_0174_ZO.html
or, in non-lawyer speak:
sawed off shotguns are weapons used for crime. they serve no rational purpose outside crime as they are too inaccurate for hunting, to random for self defense, dangerous to everyone around them, and NOT any part of the military arsenal.
however, the fully automatic and burst fire capable M16 and CAR 15 (with 20 30 and 50 round mags...)are regular issue weapons in the "organized militia" (the army), the navy and the marine corps, and as such would therefore be considered as having a use in militia service, and thus WOULD be covered by the second amendment's protections.
Lawyered.
on a more direct and less legailistic note, as the second amendment enshrines a specific right to keep (own) and bear (carry about on one's person) arms (weapons of every description), demanding that anyone not otherwise encumbered (felons, crazy people, the clinically retarded etc...) would be an infringement of that right, reducing it to a mere privilege which could be taken away with a few minor changes to the laws you propose.
it doesnt take much imagination to envision a future dingbat congress riding high on the emotional tidal wave of... whatever... who might decide that the requirements to own arms should be set MUCH higher, so high as to be unattainable by anyone.
nor does it take much imagination to envision a future despot declaring by executive order that the requirements to own arms are now "membership in the ruling party" just before he declares himself El Presidente For Life. after all, thats what Fidel Castro did...