Best theory posted here yet. We need to confirm it was steel targets, but look at the "injury" closely, the spot the arrow is pointing to, is is wiped lead, look at the cut on the base (oval red), that could be a bullet hit. When a FMJ bullet hits steel, the jacket usually disintegrates and just lead is left. The OP had a pic of the bullets in his mag. I believe he said a piece hit his glasses too. If this is the case, God loves him.
If this is what happened, then poor quality, good quality, grade 8 screws etc. make no difference.
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