I think it's legal to ship if you label it ORM-D but none of the common carriers will accept it.
I have shipped ammunition via UPS with no problem at all. You just can't ship it from one of the storefronts, you have to take it to a shipping hub.
You do have to label it properly, I found a label online and printed it.
Storefront shipping locations are usually not owned by the actual shipping company nor staffed by employees of the shipping company. They usually don't know the rules and therefore reject anything out of the ordinary. If you go to a location owned and operated by employees of the shipping company there is almost never a problem with shipping anything that is legal to ship. If there is, ask for a supervisor.