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Okay, I was hoping that the 1601 was a part number of a specific barrel assembly, with a known twist rate. I may have the dealer order one in the configuration I want. I think I want one of the longer rails.
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For FN made barrels onward, 1601 would be a date code. Sixteen being the year made, i.e. a 1301 marked barrel is a barrel made in 2013.
On the first batch of US made 1/7 barrels, there was a "7" stamped on the barrel in the area between the chamber and gasblock in line with the other markings. The second, and much later, batch of 1/7 barrels were made shortly before FN stopped making barrels for Steyr, and do not have any markings to indicate that a particular barrel is 1/7. They did come with a twist designation on hang tags looped through the muzzle though.
If you are wanting an AUG in a specific configuration or color, including 1/7 twist, a typical dealer will not be able to help you. Your choices are the factory at MSRP or Pete Athens of pjs-steyraug.com.