I didn't notice the thread until now but just in case you are still stuck.
For nylon/webbing pouches
Fill a bowl up with hot water, stick the magazine snug into the pouch then submerge pouch and magazine into said hot water. Leave to sit for about 15-20min before taking it out and dipping it into a bowl of cold water. Leave the magazines in for a few days and periodically draw and insert a few times, you may have to repeat the process until you have the retention fit you are comfortable with. Just out of curiosity, are these WE magazines? should be a good fit as they are almost exactly spot on dimension wise (don't make me get the caliper out). This will gradually stretch the material and then stabilise the fit.
For Kydex
Insert magazine until seated correctly, borrow wife/gfs hair dryer and gently heat the pouch in areas you get the most resistance from. Have a bowl of cold water on standby to submerge it in after, again leave to sit for a while and periodically draw and reinsert magazine until your happy with the fit. Again you may have to do the process a few times but do this gradually and do not rush it, try not to distort the lips of the pouches otherwise you will run into issues, unless of course you want to form a finger lip or something.
For leather
You will need leather stretching tools and chances are it will be more trouble than its worth, I wouldn't bother or advise it.
Just out of interest, do the pouches by any chance have a kydex retention clip sitting inside them? Check to see if this is the case and just follow the guide for kydex.
Hope it helps