I have imported several guns from the UK into the USA. You need a LICENSED exporter in the UK... there are several firms that can handle this and they will also make arrangements to ship to your US importer.
If it qualifies as a GUN in the USA, you need to have an FFL licensed importer to clear it through US customs and you must have first applied for and received an import permit, or the importer must have done so. The importer might be your FFL, but probably not. The importer ships to your FFL. PITA, but might be worth it.
