After WW1 over 1 million rifles were sent to government arsenals to be cleaned, repaired and preserved. This started as early as 1919, and went throughout the 1930s IIRC.
By 1927 many of the earlier preserved rifles were found to have rusted and pitted barrels, and had to be repaired. All 3 of the makers of the M1917 had made extra barrels.
Perhaps yours is one that had a pitted barrel and was replaced at one of the government arsenals in the 1930s.
It's fun to wonder!
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