Quoted:
If we're going with NIJ rating then the esapi is level four stand alone and that video is swaying me that way.....it was hit by three different rounds with no soft armor behind it and it did just fine.....yea no AP rounds but after watching that I don't think it would have an issue .....I do think the soft armor behind it is to reduce excessive blunt trauma
I don't mean this in a disrespectful manner, but I don't think you have a very firm grasp of the technology and terminology of rifle protection plates.
First off, this needs to be clarified if not for you, then for many other people. NIJ level IV is a threat rating with specific test criteria. ESAPI plates are tested to a completely different criteria, established by the military, which is usually just referred to as being an "ESAPI" rating. The ESAPI rating is by definition an ICW rating, as I will explain below. There is no such thing as a "Level IV ESAPI" plate. There are level IV plates cast in an ESAPI triple curve shape, but the title of "Level IV ESAPI" makes no sense once you understand what the words mean. Unfortunately many use SAPI/ESAPI improperly to refer to any rifle plate.
The protocols and requirements for NIJ testing are public. If you really want to understand what the rating means, and how they are tested, then you need to go read the full PDF outlining the criteria of testing which is available on the NIJ website.
Additionally, there is enough information out there regarding the ESAPI plate testing procedure, as published by the military, that it is clear that ESAPI plates are tested as part of an armor
system which includes the soft armor behind the plate. Accordingly, when going through testing, a certain frequency of PLATE PENETRATION is allowable if there is not full system penetration; meaning of course that the soft armor catches the spall and bullet fragments which are expelled from the back face of the plate during a plate penetration.
You also would always want to be wearing soft armor behind an ESAPI plate due to the fact that excessive Back Face Deformation can kill you dead just like a bullet punching a hole in you can. You can not measure BFD by looking at a plate after it has been shot. It does not work like that. Refer to the NIJ protocols for further explanation of proper BFD measurement.
The Youtube video you posted is not very enlightening if you understand what you are seeing. 7.62x39 is not a difficult round to stop in the context of rifle plates; pure compressed PE plates stop them just fine. The benefit of the ceramic hybrid plate comes from the ability to stop the higher threat rounds with hardened penetrators, like APM2, and M855. Those are harder rounds to stop than even the mild steel core 7.62x39. Additionally, BFD is not being measured in the video, and very well may be in the realm of serious injury or lethality.
The bottom line is that ESAPI plates only attain their APM2 rating when used ICW soft armor, and it is documented that plate penetration without system penetration is acceptable under the ESAPI standard. I wish I could tell you more about which rounds out of the test battery for ESAPI plate cause plate penetrations, but it is my understanding that data like that is classified, as is the full ESAPI testing protocol. I only know what I know from reading technical reports addressing very aspects of the armor technology published on the internet from various branches of the military.