[26ND inscribed on it]
FWIW:
"26" is the bead size, 1/16" ( a larger size, 3/16", is available).
"ND" is the bead material (Ivory or Gold), and the height (7/16").
You need a higher front sight blade - but the sighting error should not be measured @ 50 yards, since the standard measuring distance for calculating sight heights is 100 yards.
It looks like your sighting error will work out to be approx 10" too high @ 100yds - so I would replace your 26ND with the Lyman VA/VF .560" tall front sight blade, with the Ivory or Gold bead in the size of your choice.
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