The BTF demon in my G19 has been exorcised!! My pistol is a G19 Gen4 MOS. I was experiencing at least 2-3 BTF's per 15 round magazine with all weights and velocities of factory and reloaded ammunition. BTW, the Apex and HRED were not the solution, so I kept trying.
First, my thanks to all the contributors to this topic who educated me. Second, my thanks to Apex Tactical Specialties for their instruction on extractor fitting.
https://www.apextactical.com/blog/in...g-fre-fitting/. The usual YMMV caveat applies, but here is what worked for me.
The main take-away from from what I learned is that the empty shell casing must be held tightly against the breech face before the ejector kicks out the shell. The Apex instructions make it clear in the description of figure 4 that downward pressure on the shell must be 3.5-4 lbs to push the shell down out of the extractor. In my instance, the pressure needed was only about 1 lb or less. I expect that tolerance stacking was the culprit. From my spare parts bin, I found an old Gen 3 non-LCI extractor, and combined that with a stock plunger and a white spring loaded bearing. The pressure required to push the shell down jumped from < 1 lb to about 4 lbs. After those changes were made the BTF went away. I have put 200 rounds down range with a variety of factory hollow points and my own 124 gr. reloads with no BTF problems. The ejection pattern is about 4:00 at a distance of 3-6 feet, depending on how hot the rounds are.
I wish you luck.