Shipping an action????

It could only be shipped to an FFL not sure about carrier restrictions. When ordering stripped lowers online I think theyve been shipped fedex/ups to my FFL

Correct. Because they are "Serialized," for the most part. They are the only part of an AR build that is serialized and, therefore, must be NICS checked before being delivered to an end customer... just like handguns and fully assembled rifles/shotties etc. All other parts of an AR are not serialized and can be sent directly to an end customer from a manufacturer. The upper can be sent directly if sent by itself (i.e. not attached to a lower).

I don't think the carrier matters if it's going to an FFL.