Importation of any weapons is suitable to import duties and VAT.
Would you have a "European Firearms Pass", make sure that all your weapons are listed in. Registration in Belgium through the local police will still be required without asking permission to transfer the weapons into Belgium.
The permission must be obtained prior to bring the weapons in Belgium.
If needed, the SFPRS can provide you with some pieces of advice.
Form 1: Request to the Governor (English and French)
Form 2 : List of your weapons
Form 3 : Statements
Form 4 : NMR's Statement
Form 5 : Dependent's consent