Only 29 usable rounds ymmv - Lancer Systems L5AWM Smoke AR-15 .300 Blackout 30 Round Detachable Rifle Magazine

I bought 3 of these mags specifically for use with subsonic rounds and overall I feel they are good quality build and materials. In both my Sugar Weasel and Palmetto State 300blk rifles none of them lock when loaded with 30 rounds, but they do lock with 29 rounds. I tried PMAG 300 Gen 2 and it also had the same issue. A PMAG 556 mag locked fine with 30 super rounds. I won’t ding the brand as the issue seems to be caused by the larger size of dedicated 300blk mags.