Afsaneh are you referring to semi-automatic weapons?
Or automatic weapons, which are indeed extremely restricted for legal civilian usage? In the US you can't own an automatic weapon made after 1986. And to own a weapon made before then is difficult and comes with a higher level of restriction, inspections and scrutiny.

"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming

Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.