I'm not sure. I would assume that it would be covered like any other possession, subject to deductible. Look in your policy for exceptions.
That said, you can get insurance for just about anything, if you ask the right insurance person. As your agent or if they are clueless, ask others agents for other companies.
A google search for "insurance or guns" and I found this:
Safari Club International Insurance Programs
And just under that, State farm might not insure you if you do have guns but that was dated in 2000.
But if you're looking for insurance in case where you use your gun, that's a different ballpark. Your liability might no cover you there. In Texas you can get that kind of insurance - look for Texas Law Shield but they only insure if you live in Texas.