Search:

Nope, firearms and ammunition are prohibited items for post and courier

But they would only being returning to sender because they refuse to deliver it - which their website says they will. It's easy to safely return a scope, stock, suppressor, etc. If they destroy it...

Yeah, but it should give you some sort of legal comeback if they fail to deliver or destroy anything you send.

According to their website, firearms parts are prohibited to send by post, but allowed by their courier service if appropriately packaged.