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.