Mag cross section - SGM vs. Magpul vs. Glock

[RickT]

Rebuilt my PCC with a Foxtrot Mike receiver (had been using Endomags).  I swung by the range last night with only a 33rd SGM mag and a 10 round Magpul.  I know SGM mags are not supposed to work and, no surprise, they didn't.  I was puzzled by how sloppy the SGM is in the magwell, the Magpul a bit less so.  I did insert a Glock mag this am and there was absolutely no fore/aft wiggle.  Hopefully the Glock mags will feed in this morning's test.  Are the SGM's slightly smaller in cross section to speed up mag changes?