Watching a recent episode of "Forgotten Weapons", Ian McCollum talked with a Brownell's representative regarding their "Retro" series. Seems that the only guns that will be continued with are their M16A1, XM16E1, and XM177 models. The Model 601 (green furniture, "duckbill" flash suppressor, etc.) is discontinued. Seems that it was never that big of a seller. As was the Model 605. They are considering an M16A2 version, although that remains to be seen.

Of course, guns can still be built from parts that Brownell's (or others) have in stock, although nowadays that may be problematic.

I would have thought that the 601 was more popular, but I guess it appealed mostly to the history buffs and similar.