Let me recommend USAA for those eligible.
My homeowner's policy has something like a $1K limit for firearms, computers, and jewelery.
I askd for increased coverage in all areas, and they were very reasonable about it. I'm not sure of the cost, but a $5K increase for the firearms coverage comes out to something like four or five bucks per year. They didn't seem to care one way or the other that I have a safe for storage.
It's very reasonable, and I'd recommend finding a carrier that will allow riders to the policy for supplimental coverage.
And, GSTN, you'd better mention it. If you don't, I'd guess that you will run into a policy limit and have your reimbursement denied.
If you have a fair amout of weapons, I'd get a comprehensive inventory, with replacement costs and photos sent to your insurer to verify coverage. Send a duplicate letter to yourself via registered mail / return receipt.