I dealt with the very same issue with USAA, and ended up giving them the serial numbers, barrel lengths, model and make of everything that was insured. I wasn't comfortable with this info being in someones data base in the event it was compromised, but having been the victim of theft before, went ahead and did it anyway.
Adding a rider to your HO policy is probably the way to go. Be sure to ask LOTS of questions, as insurance agents-either because they're crooks, or because they don't care-have been known to leave important info undisclosed. Some riders have a monetary limit, so make sure you know the value of your weapons-in other words, multiple riders might be needed. Make sure ALL causes of loss are covered in order to indemnify you.
Often times, the best rates are offered first, when paying a few dollars a year more vastly improves coverage. Auto collision is a perfect example. It only cost a little more (a couple of dollars monthly) to lower your collision deductable from $500.00 to $125.00, for example. Again, ask lots of questions (I always walk the agent through a scenerio, to make sure I'm getting what I want).
I'm not an insurance agent, but I took the property and casualty exam (succesfully), and it opened my eyes to how vulnerable an insuree is if his or her coverage is not specified down to the finite details by the insurer.
Shop around. Some companies in some states offer better rates than others, especially if you insure both your home and auto concurrently by the same company.
Good luck.