Watch the video and pause it at 15 seconds.It appears to me to be a self made self applied seam holder, it may as well be a pad under the magazine to stabilize it, or could be something else but based on the very small picture you posted, I can not get it detailed enough running on my 3840 X 2160 monitor to determine what it is.
I still think that it is there to stop the stock from splitting during auto fire. I remember people having issues with the stock splitting enough to allow the receiver to separate from the stock. It could also be an RFID chip for armorer tracking. I will go with the stock splitting tbeory.
That is exactly what it is. The stock will split with Sub Sonics also. The problem is that once it splits the first time it shaves a small amount of the inside of the stock off. It creates a ramp that makes it progressively easier for the receiver to pop out, shaving away more material each time.
I have worked on some fixes including a Ti insert but nothing I find acceptable and affordable.
FYI FNH has known this was/is an issue for many years now. This is why FNH armors keep a box full of new stocks sitting around and as soon as a P90 has this issue they pop a new stock on it.
If done right this could be a good fix!OK ...I'll eat the poisonous fruit from the tree of ridicule which subsides in " The Pit of Misery "... this morning.... " Dilly, Dilly ! "
There are design/repair obstacles on all 4 components that interface this area. Best I can do is offer up a temporary fix but it may last longer than I anticipate ??? .... the #1 problem .... aka lack of real-estate !
I have to concur with Jay, if he has tried a few options for a permanent repair ... nothing that I could come up with is easy or cheap . I don't think Jay gets enough credit around here.... !!!! JIMO
Here are some pics of a repair concept that I believe would remedy the situation . At least temporarily... for me... I would enjoy the challenge !
Some "Low Boy" or " Button Head " 6-32 or 8-32 SHCS's would be needed.
The receiver would need to be stripped and the stock and receiver re-assembled along with the ability to clamp things securely.
The Magazine would need to have the bottom side ribs cleared flush in the marked area, thus providing a little clearance for the SHCS which would need to protrudefrom the stock surface approx. 70%-50% of the head thickness.
Finally you better be good with numbers for the reverse engineering number crunch game.....LOL
There is enough real estate " meat " in the receiver at this specific location to tap some threads, the stock wall thickness is minimal thus a shallow counter-bore pocket less than the head thickness is needed . Finally ... it will require an allen wrench to field strip slowing the ease of disassembly.... for those unfortunate souls... that desire to shoot AE rounds because ...??? they are cheap ! I don't know if that is even possible ... shooting AE in your P90 ???? I would think that answer is " NOT FOR LONG ..." ! Considering some may try the A/E for economical reasons ... they will surely slip into " The Pit of Misery ".... Dilly,Dilly
Check it out.... it would allow the end user weapon usage without/stock receiver separation .... while a back up stock is procured !
If done right this could be a good fix!
Shooting suppressed with even just 5.7 197SR ammo beats up that area on the stock. I used an AAC 762SD on my SBR'ed PS90 and that area looks chewed up a little.I do have another option in mind. BUUuuuuuut I am not ready to share because it's a path I am going down that should work well, be cheap and easy to do.