I have a 40# @ 28” Bob Lee Shikari with cobra curve limbs that I draw to 40#.
I also have three other bows that I regularly shoot for 3D or other tournaments that are within a pound of the Shikari: a Bob Lee Legacy, a Black Widow PSA, and a Hoyt Satori. The Legacy and the PSA are tuned for 29” GT .600 spine Ultralight shafts with 100 grain points with 12 grain inserts, and the Satori is tuned for a 29” Victory VAP .600 spine shaft with a 110 grain glue-in point.
The Shikari is tuned for a 29” Victory VAP .500 spine shaft with a 120 grain glue-in point. So your observation is consistent with my own experience: the Shikari requires one spine group stiffer shaft than the other bows of essentially the same draw weight.
It does surprise me that you would require a .300 spine shaft for a 47# bow with about 250 grains up front, and I assume about a 30” arrow, even knowing that the Shikari requires a stiffer shaft in general, but that's the direction your tuning seems to be pointing, and I have no reason to disbelieve your results.