I've had a high mileage G17 for quite a while now. I also bought a G19 for better concealed carry. Having both, I liked the fact that my 19 could use the 17 mags. Then I got to thinking. (I know, this usually leads to trouble.) It would be nice if both pistols could use both mags. This lead to some internet searching, and then I decided to go ahead and get some tools in hand and commit to the job.