This is a Hera USA Magazine known as the H3L chambered in 223 Remington, model 13-10B.
Civilian 10 round magazine for use in semi-automatic firearms of the AR15 / M4 series. Specially made without a limiter for the California market" the H3L can neither be dismantled nor converted. Enables legal training with the feel of a 30 round magazine in various US states.
Features:
Polymer
Fits AR-15 and similar platforms