Followup, the bore diameter measured with precision pin gauges is .243" go and .244" no-go on both ends. (no choke). The JSB Knock-Out slug is .2505" for about 50% of its length. The JSB King Heavy pellet has a dome diameter of .247" and a skirt diameter of .256".
It should be clear the liner swage for the pellet is .007" and the heavy pellet will experience a light swage at the dome and a heavy swage at the skirt, but because of skirt taper, the swage length is relatively short. So, liner /projectile resistance will be quite a bit higher for the slug than the pellet of almost identical weight. My takeaway from this is that the slug will benefit from a wax lube and probably have a slower muzzle velocity than the heavy pellet. I predict excellent accuracy of the heavy pellet and not quite as good accuracy with the slug. Of course the slug advantage is a much better BC of .092 (advertised). Only testing will tell.