My shortened Royale 500 does well at 50 yards and so so at 100 yards, but I lose 40 % or more at 150 yards and beyond.
I measured one of those Kings, it measured .247 on the head and .254-255 on the skirt, but as you know they are hard to measure.
I just slugged the 4.5 inch breech portion of my Royale 500 I cut off to make it the same length as my Royale 400, the rifled section is on its way to AOA on the barreled action to get a Elite regulator, so I can't slug it. The smooth section slugged out at .250.
I wrote you a message about this on your TAG post, about the cast bullets and cutting off chokes. I have found the choke was a detriment to my personal air gun cast bullets venture. I found the groove diameter is the diameter you want your cast bullets to be for optimun air gun accuracy.
One of my 25 LBT rifles, the carbine, I can shoot Kings thru by pushing them past the lead cut for the .255 diameter LBT's at which point I feel resistance. That 17 inch barrel shoots better with Kings at 915 to 950 FPS, since I bobbed the choke off. It slugs at .255 which oddly enough is what the King skirts mike out at, so go figure.
Great work Ted.