As I recall "Not for Ball" during the era in which this stamp was used was required on any barrel with at least .008" of choke constriction. This gun likely had less than full choke & then was jugged to give a tighter pattern. Could have been done when built or at a later date either, hard to tell. With the Not for Ball stamp it would have had at least that .008" of choke when proofed. From the picture it certainly does not appear to have been cut.
"Normal" choke with the Not for Ball stamp could have been anything from around a � choke all the way up to full. An I/C choke would not normally have required it. A � choke of around .008" to .010" was quite popular for driven shoots in England.
"IF" it shoots good, enjoy it & don't be overly concerned about it.
PS; 13 = .710" & 14 = .693 or a difference of .017". The difference could however have been less than that even. The bore could have just "Barely" accepted the 13 gauge plug & the choke accepted the 14 gauge plug with more liberal clearance. Too often we look at these early markings & take them as "Exact" measurements, but my understanding is they were not. The Proofers simply had a set of plug gages & the bore & chokes were stamped with the largest one which would enter to the required depth. The bore gage as I recall had to enter to a depth of 9". I have not seen data for the choke gage, but assume it just had to enter the muzzle.
Last edited by 2-piper; 04/05/18 07:56 PM. Reason: added more info
