This is an old topic, but the 20 round curved Mini-14 magazines with the plastic base plate held in with spring loaded pins are original factory Ruger AC-556 magazines.
They were made by cutting down the 30 round magazines until Ruger got the tooling to make 20 round mags from scratch. They work great and are somewhat collectable. I have several of these, two of them came with my 1977 vintage series 180 Mini-14 that was originally sold to police.
Last edited by CAR; 01-03-2012 at 02:24 PM.