Does anyone know the barrel length on the John Brown rifle ?
I don't have the barrel length; as best I recall it was about the length of the rifle I was shooting most at the time (a Henry copy with a 39" barrel).
FWIW, the barrel of the other full-stock Hawken I mentioned earlier measures ~41 3/8" from the face of the breechplug to the muzzle. Depending on which flats you measure, it is ~1.19" at the breech tapering to ~1.06" at the muzzle. Twist is 1:48, bore is .52-.53".