Unless you live in a state the requires you to register your weapon, you don't have to. If it does, contact your local police.
No, it is not legal to purchase gun magazines without a license in California.
no, if your gun is below the legal muzzle velocity which is 12 ft/p/lb [12 feet per pound of force]
No.
No.
Only NFA regulated items. For a typical rifle or shotgun, no.
With a license, yes.
There are semiautomatic versions of the Tommy gun (Thompson sub-machine gun). They are legal to own. A fully automatic Tommy gun is legal in Texas only if you have the federal license.
It is legal if you have permits for the gun and only in certain areas.
Legal age to buy a rifle or shotgun is 18. 21 for handguns.
Gun laws are dependent on your State. In Texas there is no requirement to register or license guns. A person who carries a gun on their person must have a Concealed Handgun License (CHL), but not the gun itself. It's legal to have a gun in your car without having a CHL.
You will need to define assault rifle, and where you live. A TRUE assault rifle is a machine gun, and transfers of them are tightly regulated by the Federal government. What most people CALL an assault rifle is nothing but a semi-automatic rifle, and in most of the US, does not require a license to possess.
The AK55 was the AK47 rifle, manufactured under license in Hungary from 1955 to 1963.