The search for this information took about thirty seconds (including two slurps of coffee.)
http://www.custom-glock.com/magtech.htmlThere are two basic and easy methods for taking apart your mags, we will discuss both.
Always wear safety glasses when disassembling magazines.
Method 1:
Insert a punch or similar item into the hole in the floorplate to depress in the inner floorplate.
Then take the rear corner of the floorplate and press against a hard surface like a desk until you feel the floorplate slide past the ears on the mag tube.
On newer mags there will be an audible click.
With you thumb covering the base of the mag tube slide the floorplate off while you thumb retains the spring and inner floorplate. Carefully release your thumb and remove the inner floorplate and the spring and you are done. Be very careful when doing this as the retainer and spring can come flying out of the mag body at high speed.
I prefer this method for new/tight mags and for 10 round mags.
Watch a video of method 1
Method 2:
Insert a punch or similar item into the hole in the floorplate to depress in the inner floorplate.
Put the thumb of your left hand against the front of the mag tube and with your right hand pull the punch forward. The floorplate will slide forward past the ears.
On newer mags there will be an audible click.
With you thumb covering the base of the mag tube slide the floorplate off while you thumb retains the spring and inner floorplate. Carefully release your thumb and remove the inner floorplate and the spring and you are done. Be very careful when doing this as the retainer and spring can come flying out of the mag body at high speed.
Watch a video of method 2
There is no need for a vice, pliers, clamps or any tools other than a punch or similar object to depress the inner floorplate.
Now, I'm no gunsmith but I'm willing to bet that most pistol mags are assembled in pretty much the same way. If the manufacturer wanted to make a fifteen round mag a ten round mag it probably works much like the magazine tube of a shotgun to keep the follower in. There would be a detent in the stamped metal the impedes the follower from moving far enough down the mag to accept more rounds. A drill bit and a file could change that in about two minutes.
An act of Congress takes a helluva lot longer. *Corrections and elaborations regarding the technical aspects of this post are warmly solicited from those who know more about it than me. There should be many.