There were assualt rifles at the time the country was founded, they were called muskets, Penna. Rifles, Kentucky Rifles or Brown Bess. The same rifle that put game on the table was used to keep marauding indians, Lobster Backs(RedCoats and hungry bears at bay.
There never has been a Constitutional right to own landmines live hand grenades etc. Machine guns have been severly restricted since the National Firearms act of 36 was passed. It IS legal to own one but there is the little matter of an ATF permit. For the record, no lawfully owned machine gun has ever been used in a crime by the lawful owner. The price of such weapons is far beyond the means of most gun owners, including me!