Pretty sure there is no one left alive who knows what these codes on the bottom of the barrels mean.

X
K
E
A1 on a 1909 vintage KE-Grade 16-gauge --



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K
E
Y on a 1906 vintage KE-Grade 12-gauge --



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F
E
G
13 on a 1906 vintage 12-gauge FE-Grade Trap Gun --



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M on a 1906 vintage 12-gauge CEO-Grade --



X
O on a 1905 vintage 16-gauge DEO-Grade --



P
A on a 1896 vintage 12-gauge AE-grade --



B
J
E on a 1895 vintage 12-gauge BE-Grade --



We can make guesses on some of them, but many remain a mystery.