I don`t own one
The answer can be found here: http://www.remingtonsociety.com/rsa/questions/barrelcodes
The letters AT indicates that your H&R shotgun was made in the year 1979.
1000
The letter I think
here is a link to determine the age of Remington's http://oldguns.net/sn_php/remdates.php
IF your shotgun has the original barrel, it can be dated ffrom the 2 or 3 letter code stamped on the left rear side of the barrel. The website for the Remington Collector's Association has a chart showing relation of the letter code to month and year of production.
Date code stamped on left side of barrel, go to Remington Society of America for diagram and chart.
I am by no means an expert, but my first shotgun was a used Remington 1100 sportsman 12ga shotgun w/ fixed full choke. I bought it at a local pawn shop in good condition for $300. This was about 3 years ago. New, they run about $800 so it depends on the year and condition but $300-$400 used is about average. Hope this helps.
If you have a light weight browning auto-5 shotgun,then the serial number should have a Letter L,or a letter G prefix to your serial number.If the letter is L then your shotgun was made in 1956.If your letter is G,then it was made in the year 1958.If you do not have a letter prefix to your serial number,then you have a standard weight auto-5 shotgun which was made in the year 1927.
In the year 2013, 1100 A.D. was 913 years ago.
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