[wterrell]

Refreshing of the rifling in the field.
Straightening of the barrel in the field.
Removal of blockage of barrel in the field.
Repair of the 'unknown' in the field.
The witness marks were for the benefit of gunsmiths unrelated to the manufacturer/arsenal.
The very same purpose as a 'jack' with a new auto. Ford Motor Co. or Chrysler Corp. does not need a 'jack' but the owner does.

But Mr. Simpson could enlighten us in short order if he would post a reference or two.