This is a 17 WSM not a 17 HMR. I am going to have to talk to the gunsmith who did the rechamber, I think snapcrackpop is on to something. 1 in 9" twist is used on a lot of .17 call centerfires that have no trouble stabilizing a 25 grain bullet. I think there may be more than bullet weight causing the bullet to tumble, but I am interested to hear what snapcrackpop has to say.
Thanks