Scott,
There are certainly customs issues in doing this and most probably legal ones as well.
When departing from the US, I cannot remember if you need to apply for a permanent weapon exportation or just be asked to fill out a permanent weapon exportation form at the airport, however any weapon being exported permanently from the U.S. has to be declared as such. Some fees or taxes may be involved, as well as proof of ownership... Call the U.S. Customs & Border Protection to find out the exact procedure or check out their website at
www.cbp.gov for information. Proof of ownership or a paper
When arriving in Namibia, you are required to declare all firearms no matter what, failure to do so may result in more trouble than what the favor is worth in the first place. Anyhow I do not believe that as a foreigner you can permanently import firearms into Namibia and if it was for someone else, a citizen of Namibia, I do not know the regulations on that. Certainly at a minimum customs duty will have to be paid on the value of the rifle and an invoice will be requested by custom officials. Contact the Namibian Embassy in the U.S. at
www.namibianembassyusa.org so that they can answer your questions and let you know of the proceedings.
This is not an area that I know so much about, so I strongly suggest that you get your information straight from the source.
When you find out if and how this can be done please check back in and let us know.