In the Anushasana Parva of the Mahabharata, just like in the Shanti Parva, Bhishma gives advice to Yudishthira and concerning how to be a good king and how to be good person, while he is lying on a bed of arrows after the end of the Kurukshetra war. In this chapter, Bhishma tells Yudhishthira about various actions which are rewarded and punished in the afterlife. One part of the list seems rather peculiar to me, though:
śastravikrayakāś caiva kartāraś ca yudhiṣṭhira
śalyānāṃ dhanuṣāṃ caiva te vai nirayagāminaḥ
They who sell weapons, they who forge weapons, they who make shafts, and they who make bows, have to sink in hell.
So my question is, is it always a sin to make weapons?
Is the verse just saying that people shouldn't go into a weapons-making as a business? Or is it actually saying that it is forbidden for anyone to make a weapon under any circumstances? It would be rather strange if making weapons is categorically forbidden; how in the world would Kshatriyas get the weapons they need then?
Do the Manu Smriti or other Dharma Shastras shed any light on this?