His 5/16x14 compression joint/insert didn't fit a standard 5/16x14 Carolina Custom butt I had. They seem to be a bit thicker. It would only take the first 1-2 turns after that it was a no go lol.
I wouldn't be surprised if that's exactly what's going on with the OP. I actually had Dennis swap out the insert on a 30" 314-3 shaft with his compression insert as an extra shaft for my Searing, the original predator insert just didn't feel/hit the same.
I would probably suggest the same as above by Amphibika suggested have the shaft insert changed.