So still no answer to my question? No one has any clue what kind of restrictions we could place on gun ownership in the US that would not violate the 2nd amendment, but which would be effective at preventing these kinds of shootings. But somehow I'm wrong to point out that if you can't do this, perhaps you shouldn't argue that "restricting gun ownership" is the solution. Strange. Very very strange.
1. Acknowledge that we (the US) have a "gun problem". Yes, there are other factors involved, but those factors don't take away from the actual gun problem. Yes, gun control affects "law abiding citizens" unfairly, but so do every other law created. Furthermore, every criminal was once a "law abiding citizen" and legally purchasing a firearm doesn't make you a "law abiding citizen". It means that you legally purchased a weapon, just how a thief legally purchased gas to fuel his car. Therefore, the term and concept takes away from the problem.
2. Determine what types of firearms should be accessible to the general public. This needs to be generalized across the nation. Allow states to add to, but not allow to take away. Realize that the average person does not need access to weapons with large magazines, certain automatic settings, etc.
3. Ban the production, buying, trading, selling, importing, etc. of the aforesaid weapons.
4. Implement a national background check to include factors such as people living in the same house.
5. Standardized national necessary gun training for purchase. States can add to, but can not take away.
6. Out of state purchases will be treated by the laws of the sellers home of record listed in the database and proven by the seller at purchase.
7. Implement new and enforce current auditing for gun vendors to include a database correlating with the national background check.
8. Implement and conduct an UNANNOUNCED
Don't Ask Don't Tell gun buy back program at a later date. Add benefits like a tax write offs to people to return guns that were banned.
9. Any possession of illegal weapons will result in "harsh" punishment. For example 5+ years in prison based on the weapon. This excludes weapons in the buy back program but includes vendors caught in buying/selling illegal weapons through audits.
10. Implement strict "gun-free" zones in high crime areas which include rent-a-cops (job creation Hooah!) and metal detectors. Implement "show me your papers" metal detector searches during certain hours and certain places (i.e. 2200-0500 at the park, car-wash) with stated signs.