My Prod is all stock. I have tried H&N FTT 5.53, 5.54, and 5.55. Admittedly I need more testing, but best one so far, although not by much, turned out to be the 5.55. In any case, any of the FTT's shot much better than JSB 18.1, 15.9, or any other I have tried. Maybe you can test the "bad" batch in another known gun and see how they do...