It's a 10 rounder that can be converted to a 30 rounder - Hexmag Series 2 AR-15 5.56x45 10 Rounds Rifle Magazine

Works great, no feeding issues. Compared to the series 1, the series 2 feed lip design closely resembles a PMAG's feed lips, that's a good thing. If you visit or move to a free-state, you can easily convert it to a 30 rounder by drilling out the rivet on the floor plate, remove the floor plate, remove everything inside, grab a 30 round mag spring and utilize the existing follower and spring-floor-plate, slide them in, slide on the floor plate. Tada! you have a 30 rounder. I suggest using Wolff mag springs, they come in 2 and 10 packs.