I'd put in your comments import codes
93040000 (air guns)
Or 9305 parts and accessories.
With a document licence code of 9020.
"This product is exempt as it does not meet the definition of a firearm, component part of a firearm, ammunition or a restricted firearms accessory as detailed in...
Just spent a month in UPS limbo back and forth with the RIF / invoices showing what it was. (B-11 foregrip for AK74su).
Then I get an e-mail 6th June 9:40
Blah Blah Blah
"As a matter of urgency, please provide us with your clearance instructions; including:
Customs query: Under declaration...