"Any individual may ship to any Federally licensed dealer without restrictions."
The level of authentication required is at your descretion. If you're comfortable that where the rifle is to be shipped is in fact a 01 FFL holder, that's all you really need. That being said, some shippers want assurance that the rifle is going to a licensee. again some do, some don't.
For any interstate transaction, a FFL holder IS required. In state can be considered face to face.
The outside of the package shall not be marked in a mannor to indicate that there's a firearm enclosed. When the "contents" portion is filled out, I usually put in something to indicate, but not give outright disclose the contents. ie: xm15e2s#123456 for Bushmaster XM15-E2S serial number 123456. This information may or may not appear, depending on the company.
IF you have a Federal Express depot nearby, do yourself a favor and set up an on-line account, it's not difficult and has no minimums. Log in, fill in the blanks, print the lable and drop off the package...no questions., no hassels.
The Post Office will only ask if you want insurance and if there's anything breakable, flammable, perishable,.. Seldom is there a need to disclose the contents.
Pack the rifle very well. Seperate and wrap the two halfs well with paper and tape. It should take you fifteen minutes to wrap, and the recipent twenty to get it un-packaged. One way is to buy a hard case, and ask for the box the case came in. Case the rifle, and put the case in the box. Bigger, better, and stronger is the motto for packing guns. YMMV