It’s designed for gen 2/3 pmags, the insides are moulded to fit the raised grid pattern and lock into the the 5 groves running down the front and rear.
If it’s a PMAG style not the smooth EMAG type, should fit…
My “gmags” are G&P gas mags, bloody heavy (iron) and off spec so they don’t fit perfectly but they’re not going anywhere once tightened down.