Peace Dollar Experts....(or anyone who knows the answer)

Does anyone know why - or what causes the long single line scratches that I have seen on more then a handfull of MS Peace Dollars? These lines are (seemingly) always at the bottom of the neck of Liberty.

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Comments
Liberty: Parent of Science & Industry
Would you personally pay a premium for it?
1922
1922-D
1923
1923-D
Check out my PQ selection of Morgan & Peace Dollars, and more at:
WWW.PQDOLLARS.COM or WWW.GILBERTCOINS.COM
you can occasionally find really nice, advanced stages of that same die crack.
K S
There isn`t anything more I can add to what has already been said.