Tocho, here's a summary, off the top of my head:
Can't buy any firearm if under 18. Can't buy a handgun if under 21.
Individual buying a long gun (rifle, shotgun) from licensed gun dealer: Federal background check via database (10 minute process conducted by dealer over the phone).
Individual buying a handgun from licensed gun dealer: Federal background check via database (10 minute process conducted by dealer over the phone), but the individual must reside in the same state as the dealer, or the handgun must be transferred via a licensed dealer in the buyer's state of residence.
Individual buying from another individual, both resident in same state: Varies by state. In Georgia, this is a private, unregulated transaction. However, you cannot knowingly sell a gun to someone who is barred from owning it, for example, to a felon or a youth, since it would be a federal violation, as well as a potential state violation. In other states with stricter laws, you cannot sell directly to another indivdiual. A licensed dealer must be involved and background check conducted.
Individual buying from another individual in different state: Gun must be transferred to a licensed dealer in the buyer's state of residence, for transfer to buyer, Federal background check conducted as if the buyer is buying from the dealer.
Misc. stuff:
Fully automatic weapons are legal in some states, but a special application, extensive background check, and special tax are necessary.
In many states, law abiding citizens can get a special class of federal license (Collector of Curios and Relics) that allows them to directly purchase guns classified as "collectible." These are usually guns 50+ years old, mostly from WW2, WW1, etc. To get this license, you go through an extensive federal background check, have to notify the local chief law enforcement officer, and maintain a collection logbook. You can't be in the business of selling these guns for a profit. You are subject to audit by the Bureau of Alchohol, Tabacco and Firearms.
Each of the 50 states has laws regarding ownership of guns, usually mentioned in the state constitution. Some, such as New Jersey, require a permit for each gun. Some, like California, have waiting periods (usually a week) from order to delivery.
Each of the 50 states has laws regarding the manner in which guns may be carried (open, concealed, etc.), and where they may be carried (not in courthouses, public buildings, political gatherings, etc.) About 2/3rds of the states have some sort of licensed concealed carry.
Many states have reciprocal agreements regarding a citizen licensed to carry a concealed weapon. A person licensed to carry a concealed weapon in Georgia has reciprocal privelages in about 20 other states.
But, the bottom line is this: No matter how many gun laws we have (and we have a lot), criminals don't obey them. They only limit what law abiding citizens do.
A good case in point relative to the tragedy that occured in Montreal: In most states, schools are off limits for carrying a concealed weapon. Think about what happened: The 20 innocent people who were assualted were all unarmed because they were obeying the law. The one armed person was a criminal.
A similar event occurred at Pennsylvania law school a few years ago. The attacker went on a rampage and was eventually subdued by law abiding gun owners who retrieved their guns from their vehicles. Harm was done during the time it took to get those guns from vehicles.
When you use the law to disarm good people, evil people arm themselves, regardless of law, and do harm to the unarmed good people.
They'll further toughen gun laws in Canada in response to this attack, and the net result is the good people become even more vulnerable.
