I am using TTI pads and had the same problem. I read somewhere on this forum to lightly round off the top rear area of the mag. I LIGHTLY hit it with a Dremel and they fit. I'm a coward so I tried one mag only, it fit the gauge, ran some rounds through it and was satisfied. They all fit now.
Some what related note... A friend was working a chrono stage at a level 2. They bumped two people to open because the mags didn't fit the gauge. Both shot 320's.