I have a small collection of older Autococker barrels, many of them J&Js in various configurations. I recently recieved what I initially believed to be a stainless J&J as part of a package but there are a couple odd things about it. First, it has the same porting as my other J&J stainless but it does not have the typical ring for a cocker shroud that all my other J&J barrels have. Second, it is stainless from breach to muzzle on the interior, but the stainless is very thin at the breach end and there is what appears to be an aluminum sleeve pressed over it that is threaded for AC. My other J&J is machined from one piece of SS from end to end. It also has what appears to be the remnants of a J&J sticker near the muzzle, also different than any of my other barrels but I don't think that is as significant as the first two points. I'm assuming this is stainless steel because the porting matches my other barrel I know to be stainless steel and it is shiny like SS where most J&J plated brass barrels are a matte finish. However, perhaps it is chrome plated brass, it feels slightly lighter than I think SS should feel. Any idea on what it is exactly? Is the aluminum sleeve factory or the work of a skilled machinest to convert a barrel to AC threads?
Here are some poor pictures (my batteries died so I could not get better).