My experience with a Kielwood shaft, Jacoby, I only have one. The shaft, dark roast radial 30" 3.5 oz, was a little too light in balance up front for my taste. I drilled and tapped in for a short piece of 5/16"x14 pin of .3 oz to give it a slight more forward balance for my preference. My feeling is that with this combination I get the weight I want without the front end weight of a shaft that was naturally at 3.8 oz. Also I tapered it down to 12.5 mm from the 12.75 mm as received just so it matched my other shafts that I was used to.
As to whether the front end is cored or not, or does it have lower deflection than my Jacoby Ultra shafts or Rhino carbon shafts, I am not qualified enough to tell you. I will say that I shoot all three without any compensation.
I changed the tip to an Ultraskin black med like I have on my Ultra wood shafts, but changed it again to a black soft as the hit was too harsh. I am considering going softer yet to an ultraskin pro as even with the soft it is still harsh. The shaft has an incredible amount of energy transfer, even more than my carbon shafts. The shaft has a finish that feels hard and similar to a carbon shaft.
That's all I've got on my one Kielwood shaft. Your views or experiences may be different and that's fine, but these are my views on my shaft.