Can lay people be involved in the weapons business?

There is a short sentence in the suttas where the Buddha said lay people should not involve themselves in the weapons business, but it seems this is not as serious as the five precepts. The question is, how much is considered weapons business? For example, is getting involving in the armor business considered weapon business? What about selling weapons designs, technologies, intellectual property, etc., but not selling weapons themselves? What if someone is only skilled in weapons/war and cannot make a living off of other professions?