vacuum and surface tension are the two properties at work here that hold the gear back against gravity. The trick to being able to invert the amp is knowing where to break the top off. You need to leave the smallest part of the neck intact as well as a little above it. From there it is pure physics. Most people are unaware that you can turn the amp upside down and withdraw, and have always held it right-side up which usually dulls the pin because it scrapes across the bottom. To counteract this they will change needles or use a filter, but turning it upside down negates both of these requirements. So play around with the snap point, oh and NEVER put air into it. Once an air bubble goes into the inverted amp it'll come rushing out. Good luck.

For it to break off clean what I do is file down the ring with a nail filer and it snaps off easily and perfect. I have never heard of turning them upside down and I dont see the point

You can use the pen cap trick to crack it open, or just take some tissue and wrap it on top of amp where you would hold to crack and also on bottom, then snap. Opening amps are tricky, I have crushed a few of them last year during my first cycle. Its very frustrating to crush pharma gear and see glass all in your hands lol. I like to take a blade and softly just run it over the white strip where the amp is suppose to break off.