If you've already had "help" over the years by others you probably already have a pretty good idea of its worth.

If your gun is in high condition this is what I would recommend you do, it will take some balls to do, however. List it on gunbroker.com, start it out at 99 cents with no reserve and watch the games begin! There will be a feeding frenzy and you'll then find its true market value---and it will probably be more than you expected.