44AMP- I cant speak for the US Legal system, but applying the principles of our common law system I dont belive that the use of poison or toxins on ammunition to be used on persons is ever legal.
In a combat situation - that is war- poison ( which includes gas) is an illegal method of warfare since I think the Hague Convention. Military force can be used to overwhelm the enemy and no more, and posioned projectiles are similier to no detctable fragmentation weapons.
In a defensive shooting situation, your right to act in self defence ends the moment the threat to you does. Once the danger has passed, your ability to injure or kill others does as well. A projectile that causes injury hours afterwards does not fit into that parameter.
I think. :>)
"Beware of the Man with one gun...he probably isnt into guns enough to be safe with it".