I just realized I performed 1 other item before this last BTF test. Round count was at 200 and I detail cleaned the grooves in the slide where the slide rails travel. I didn't care if I removed any copper lube, I just wanted them spotless. Needless to say, a lot of black came off on the cleaning patch. I wonder if it was buildup from the new top finish Glock is using on the slides. Could that be slowing the slides down enough for BTF?