Well almost a year later swapped the upper onto a well used lower and swapped bolt carrier groups with one that didn't have the M-4/M-16 bcg and had previously loosened the gas block to check for port to port alignment and it appeared to have been aligned.
It went from never feeding to 4-5 hiccups out of 20 rds, will order a Nemo buffer spring specifically engineered for .300 blackouts and hopefully that will get me to 100% reliable.
Mike
