Here are some dimensional data that may help:
I had a chance to measure 2 cylinders for original 1858:
Length 2.008", dia 1.626", pinhole dia 0.266"
Length 2.008", dia 1.627", pinhole dia 0.268"
Modern BP Cylinder length:
Pietta C&B 2.017"
Uberti C&B 2.000"
Pietta conversion cylinder 2.014"
Uberti conversion cylinder 2.000"
Cylinder diameter:
Pietta C&B 1.593"
Uberti C&B 1.601"
Pietta conversion cylinder 1.624"
Uberti conversion cylinder 1.624"
Cylinder pin hole:
Pietta C&B 0.276"
Uberti C&B 0.276"
Pietta conversion cylinder 0.2785"
Uberti conversion cylinder 0.278"
Cylinder chamber diameter:
Pietta C&B 0.446"
Uberti C&B 0.449"
Pietta conversion cylinder 0.4525"
Uberti conversion cylinder 0.453"
Cylinder bolt width:
Pietta C&B 0.156"
Uberti C&B 0.160"
Pietta conversion cylinder 0.160"
Uberti conversion cylinder 0.158"
Opposite chamber face to face ID:
Pietta C&B 0.548"
Uberti C&B 0.549"
Pietta conversion cylinder 0.546"
Uberti conversion cylinder 0.541"
Opposite chamber face to face OD:
Pietta C&B 1.440"
Uberti C&B 1.449"
Pietta conversion cylinder 1.451"
Uberti conversion cylinder 1.448"
Best approach is to measure your original and purchase closest match accordingly.