Liability for unlawful possession of weapons

I heard that storing weapons or ammunition without the appropriate permit can result in a real prison sentence. But if, for example, after service or during hostilities, I kept a weapon and I keep it at home simply for self-defense, not even using it, is it possible to avoid criminal liability if I voluntarily surrender it to the police? Will it still be considered a crime, and what exactly are the consequences for such storage without a permit now during martial law?