Banjo B♭m7 chord (Double C)B♭ minor seventh on the 5-string banjo: 5 6 8 8, and 2 more shapes

Frets, string 4 to string 1: 5 6 8 8 (from the 5th fret)

1. String 4 (C): 5th fret, index finger, F
2. String 3 (G): 6th fret, middle finger, D♭
3. String 2 (C): 8th fret, ring finger, A♭
4. String 1 (D): 8th fret, little finger, B♭
5. String 5, the short g: open, G, not in the chord

Sounds: F D♭ A♭ B♭  ·  B♭m7 is B♭, D♭, F, A♭ (1 · ♭3 · 5 · ♭7)

The 5th string: the short g rubs against the A♭ in this shape, a semitone away: some players let it ring, some skip it.

Double C tuning: gCGCD, the short 5th string first, then strings 4 to 1.