Retry factory ammo. I had some problems fireforming for my ackley when four of the NEW LAPUA bass was undersized compared to the rest of the same lot of brass. I cured those cases by loading long(into the lands), went bang. Check your headspace. Make sure your primers are seated all the way. Buy a new spring. One guy on here installed a spacer/washer in the spring pack to increase the spring pressure. someone else had something dragging by the sear(?) causing FTF. Keep at it, let us know the cure.
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