If it says "Not For Ball" it means it should not be used with a Bore Fitting Ball. this had been the common size balls used prior to choke boring. It is still OK to use it with a ball which is small enough to clear the choke. This has been being done ever since the development of Choke Boring. The confusion over this was the reason the "Not For Ball" was dropped from use & replaced by the simple word "Choke". Regardless of how the barrel is marked just make certain the ball will go through the choke without creating an obstruction & their will be no problem.
All this can be found in W W Greener's writings of well over a century ago. One would think it had surely been settled by now.Old reloading data from Ideal etc recommends using a 14 gauge ball in a 12 gauge gun with choke.
