With the serial number that you provided,your Winchester model 42 shotgun was produced in the year 1938.
You are the only one that has all of the necessary information that will have to be used and reported on your income tax return for the year in order to do the calculation for the numbers that you are looking for. When you complete your income tax return correctly then you will have the numbers that you want available to you. If you would like to do some estimated tax calculations you would need to go to the Internal Revenue web site and use the search box for 1040ES go to page 6 for the 2009 Tax Rate Schedules and page 5 for the worksheet. You are welcome to try any of the calculators for some estimates to get an idea of what things may look like after using the correct IRS forms and compare the numbers. Use your search engine and type ESTIMATED TAX CALCULATORS and you will be able to find several of them that you can use for this purpose.