I primarily made this video for Marty Thompson, known on YouTube as Backyard S.C. Shooter. Please check out and subscribe to his videos because he's a great guy and you will learn a lot! Anyway, if you watch the video, you can see that doing an undercut is not rocket science. Don't bother sending out your Glock and spending big money to do this. Buy yourself a Dremel, maybe practice a little bit on a piece of wood and then do it. It might not look like it was done at the factory, but no one cares! It's a firearm, not a gold watch! Have fun and enjoy!
Here's a link to Marty's YouTube channel..
https://www.youtube.com/channel/UC-Ko4g1NEZX8TtwYA72jzyw