Nothing contained in this article shall prohibit or interfere with:
(1) The possession of a machine gun for scientific purposes, or the possession of a machine gun not usable as a weapon and possessed as a curiosity, ornament, or keepsake; and
(2) The possession of a machine gun for a purpose manifestly not aggressive or offensive.
Provided, however, that possession of such machine guns shall be subject to the provisions of § 18.2-295.