Please, try the following:
curl -X DELETE -d "bulk-delete=true" -i -H "X-Auth-Token: $AUTH_TOKEN" -L "http://openstack.cloud.public.ip:6780/swift/v1/my_container"
also we can use POST method with the same arguments:
curl -X POST -d "bulk-delete=true" -i -H "X-Auth-Token: $AUTH_TOKEN" -L "http://openstack.cloud.public.ip:6780/swift/v1/my_container"