Ah, wonderful. Turning in firearms is the dumbest fucking idea you could ever have.
Suppose you're in Germany, your grandfather died and you inherited the house. In the attic, you find a shotgun. Not that odd, since up until the 70s it was legal and normal especially in rural areas to own one for hunting.
Even if you're a gun owner, you're not allowed to keep it, since it's not registered, let alone registered on your card. You'd, technically, have to turn it in to the police. Bad idea. They won't believe your story and get all up in your shit for sure. Keep it or even better call your lawyer to hand it in.
If you're in a gun club that's cool they can spin a few things for you. You'll keep it and when a member dies they will just claim they inherited it from that member and get it registered and you can claim it from them. You may keep other gun owner's or club owned guns at your place no problem as long as it's registered somewhere and not registered as stolen.
Braun der Geist und braun die Seele, eine braune Bruderschaft, in uns brennt die Schwarze Sonne, das Symbol der Gegenkraft.