From Guns.com:

Many people assume guns are covered through the personal property clause on their homeowner’s or renter’s policy. You may indeed have some coverage there, but specialty items like guns, jewelry, and collectibles are severely limited. For example, my homeowner’s policy covers only up to $2,500 for loss by theft of firearms. I don’t know about you, but that’s not nearly enough to cover my entire collection.

Depending on the carrier, you can add a rider to your homeowner’s policy, but the coverage remains limited and comes with many exclusions. It is best to purchase a separate policy specifically intended to cover firearms.