Nothing contained in this article shall prohibit or interfere with the possession of a “sawed-off” shotgun or “sawed-off” rifle for scientific purposes, the possession of a “sawed-off” shotgun or “sawed-off” rifle possessed in compliance with federal law or the possession of a “sawed-off” shotgun or “sawed-off” rifle not usable as a firing weapon and possessed as a curiosity, ornament, or keepsake.