I have one, exactly one, CMMG mag. Came with the kit. The blackdog mags function very well and they have a loading assist tool. I've expereince the feed problem and I chalk it up tot he weakness of the CMMG mag spring. If you disassemble the mag and put a filler in for equiv of three rounds (reduces the mag cap but stops the feeding issues) then put the mag bottom back on, you might find the porblem solved. Worked for me. The blackdog mags will start doing the same thing as the CMMG after a few hundred rounds or if stored for any length of time fully loaded. Same filler trick works with them also.
BTW, the Mossberg 25 round mags have a really weak spring and need to be filled to hold only 20 rounds to make the spring stiffer at the end of rounds fed.