As SteveBny meantioned that they are tested by the manufacturer. There is nothing wrong with duplexing if you do it in the right enviroment, with the right equipment, and have the knowledge to know what your doing. If someone wouldn't have mixed two or more chemical together we wouldn't have any powder to shoot. My point is leave it to the experts and not blow yourself and / or gun up in the backyard. It's not worth it. Nothing else to say. If someone wants to takes chances and gets hurt, there is nothing I can do about it. I guess a safety advidcate with an eye or fingers missing would be more believeable.