Actually there is something. I'm not too computer savy, so I am not sure it can even be done.
You put a date of purchase on the weapon. Then you add a cost of replacement factor, due to inflation. Something like cost of gun plus say, 4 percent a year inflation.
That way, if the Remington 700 that you paid 289 for 20 years ago was stolen, you could have a fairly accurate cost of replacement factor to give to the insurance people when they asked you what it would cost.
Of course, on things like black rifles, discontinued guns, or true collector items it may not be that accurate, but it would be a good start for the rest of the stuff you had.