A few years back, there was an article in the American Rifleman that stated that many of these were factory rebarrels for various calibers. Many for south american counties that had an abundance of 7mm and 8mm. I also recal seeing .243. Also, somewhere, in my files, I have a letter from the NRA explaining this. I personally have seen one of these conversions, in 7mm. The barrel is stamped; Remington. ...
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