If you are bring cartridges into the US, you need a Form 6 issued by the ATF. They have been very responsive since moving to WV from DC, but there are some new requirements that could slow down your applications approval. It did mine.
There is a new Form 6 that must be used this year. Go to the IAA website and download the new form or they will send it back without approval.
There is a new database established into which they record all the cartridges which were imported. If you have a long list, this could take a long time and this appears to be the long pole in the tent of approval.
They seem more organized and providing a better scrub of the lists. I had listed 7.63mm Mauser Pistol from a Russian manufacturer. They knew this was the same as the 7.62x25mm cartridge and informed me that import of Russian cartridges in this caliber had been banned by Congress in 1997!!! Must be an interesting story there.
Bottom line, the ATF is doing an increasingly better job of complying with the directions of Congress on importation, and I expect the requirements to get a Form 6 approved will continue to change over the next few years.
The bottom line is to get your application in early. I’d recommend a minimum of 4 months, and 6 months before you need it would be even better. I submitted mine two and a half months before I needed it and would have gotten it 2 weeks after I needed it had I not spent a lot of time on the phone.
DO NOT EXPECT TO GET YOUR FORM 6 IMPORT PERMIT AT THE LAST MINUTE. SUBMIT YOUR APPLICATION 4-6 MONTHS BEFORE YOU NEED IT!!!