They say a picture is worth a thousand words. Here is my take on the stiff mags, I have 2 that you have to wrestle out and 3 that almost fall out. Here is the dimension across the top, from just under the little plastic wedge that sticks out, first a tight fitting mag:
Next up is one of the looser fitting ones:
The sizes (in mm) are:
Tight 75.72, 75.89
Loose 75.19, 75.25, 75.32
I think all that is needed is a bit of filing of the side of the mag with the ridge on it. The larger dimension continues on for the rest of the mag BTW. I could be wrong (it wouldn't be the first time), but others could easily check this out.