Quote
Thank you for electronic message of October 26, 2010, to the Transportation Security Administration Contact Center asking about the transport of a reloading press, a powder scale, and other items aboard commercial aircraft.
The reloading press, dies, powder scale, empty un-primed brass cartridge cases, bullet heads, rifle scopes, and bullets are permitted in checked baggage. We do recommend, however, that you carry the rifle scopes through the screening checkpoint since these items are permitted in the aircraft cabin. Doing so would afford the item better protection against potential damage.
I hope this information is helpful.
Sincerely yours,
Chad Bash
Acting Deputy General Manager for Mission Support
Office of Security Operations
Unquote
Be aware if you do bring back full rounds ("bullets") you must pre-book with the airline (max 25kg per plane, 5Kg per passenger on a first come, first served basis) and declare it on arrival back in the UK via the Red Channel (your bag with ammo should not come up on the carousel - although it does a lot of the time - but should be taken to the customs guys in the red channel by baggage control).
I also put a copy of the above letter, a note to TSA saying what is in the case and a copy of my FAC in the case.
HOWEVER
This whole issue is a hornets nest of various opinions and there are several earlier SD threads on it (do a search) and we may soon get differing opinions posted on here - but the above text is direct from Homeland Security & I have never had any problems on many trips over several years.