Why dispose your old computer then dispose your new computer? Every city has a day where you can drop off your electronic junk
Dispose of.
Since gunpowder is explosive (!) I always make sure it is made safe by wetting it - water works fine, but will also create a chemical mix that is potentially hazardous. As for the regulations in...
You burn them.
at a local household hazardous waste collection site, contact your local trash collector as rules are sightly different from community to community.