Todays performance was better, but not good enough. 15 rounds of WWB went fine, and all but one round in the last mag of 250 rounds of UMC were without issue. Still, 1 in 265 is not acceptable.
I gave the gun as thorough a field-strip cleaning as I can tonight. Tomorrow, there will be another trip to the range. Planning on 250 more rounds of UMC, 300 rounds of WWB, and 50-100 rounds of TBD "Good Stuff."
I haven't been testing the weapon scientifically, which is to say that I can't yet confidently say what is causing the failure. My gut tells me that the extractor is weak, that dirtiness makes it even weaker, and that the extractor doesn't "like" WWB for some indeterminate reason.
Tomorrow will be a "blank slate." The gun is damn clean. We will interweave mags of UMC and WWB to normalize any effects the accretion of filth might have. The "Good Stuff" should be a test for the combat readiness of the gun --- you wouldn't bet your life on cheap ammo, so if the guns FTE problems turn out to be real, but limited to cheap ammo, then it is still a worthy choice for combat. At least, that's how the theory goes.
At this point, I rate the likelihood that the gun will go out to Springfield to be near-certainty. The possibility that it is operator error is now vanishingly small, and any FTEs tomorrow will confirm this. And even if the giving the extractor extra squeaky-clean TLC eliminates my woes, the gun will probably still get shipped out for repair; I don't think it unreasonable to expect my weapon to handle 1K rounds before cleaning is required.
Stay tuned, kids --- same Bat-Time, same Bat-Channel.