The Swiss authorities online
A licence is needed to import weapons, weapons components, ammunition or ammunition components into Switzerland. The licence is issued by the Federal Office of Police fedpol.
If you enter Switzerland with arms or ammunition, you must notify an open and manned customs office, and produce the licence mentioned above. If you can produce a purchase receipt, that will make customs procedures easier. Weapons are duty free, but you have to pay VAT at 7,7 per cent on them.