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If this round was fired with the ramrod on top of it or say even with the ramrod half way down the barrel once the soldier brought the rifle up to his shoulder to fire it, then it seems possible that the bullet and ramrod could have gone down range together and embedded in the ground together, the ramrod being steel, rusted away over time and left traces embedded on the bullet. Seems a possibility.
I once read years ago and then again here recently about the muskets picked up around Gettysburg with 2, 3, 4, 5 or more rounds loaded in the barrel, soldiers never remembering to fire after loading; the result of people acting under immense stress. I have seen hunters do similar things with modern weapons acting under "buck fever".