For glocks, you can get a +2 adaptor.
However, they make an extended length adaptor for use in the KRISS weapons system. It doubles the magazine size.
Does this increase the capacity or just extend the mag a bit for a better grip.
Or if you were an “A” student in metal shop you can pretty much make a magazine as big as you want it.
You can get a 25 round mag for a Glock, or even a 50 round drum.....
This is another “gun free zone” massacre......