Excellent, detailed investigation. Do you have any lot #(s) for your ammo, that folks could watch for? It will be interesting to see if this is just a bad batch, or whether their QC has gone completely down the crapper. An important practice, which is often over-looked, is ammo inspection. Since one manually loads each round into the mag, or onto the stripper for recharging the mag, it takes almost no time at all to inspect each one. We trained that way on the PD, but even there, folks got careless. When you are standing around, ratchet-jawing w/your buds, you no longer focus on what your hands are doing. After thousands of rounds of first-quality US-made ammo, one gets relaxed. You don't scrutinize as you should. Then someone starts having feed problems, which turn out to be caused by case lips rolling over during the crimping process. Quite visible, IF you are looking for it. It can happen anyplace, anytime, w/any ammo. A good practice to adopt is to inspect your ammo before you go to the range, so you won't need to worry about distractions while reloading. It won't take long, & better safe than sorry.