JoeBob - I have an extra BCM A5 receiver extension ( what they now call "intermediate" on BCM website ), it is like new with BCM rifle spring. It has a small blemish that does not show when it is installed. It is yours for free if you want it - for your quest to get that upper to behave. That way you got lots of options for buffer weight - just be certain the buffers you try are suitable for 5.56mm in that length receiver extension ( I know nothing about 9mm buffers ). I use one - good piece of gear. I like it because Magpul MOE or CTR stocks close all the way on them if you use their extended butt pad.
I would think that would help get your bolt velocity where you want it, if it's not already. You may still have something with the ejector / extractor that needs improvement to get the reliability where you want. I don't like when empties dribble out lazy like you were describing in earlier thread, but that maybe just my OCD.
Anyway, let me know if interested