Now with the 89 grains. I had a string of shots about 6 inches across the target and the bullet holes weren't perfectly round.
Most likely cause is that you have some initial yaw which will go away at about 200 yards and by 300 yards be settled down
With all due respect, I have to disagree with Bob about these bullets settling down at longer range. It's not just imperfect bullet holes, they're shooting "about 6 inches across the target" also. That will not improve to acceptable groups at 200/300 yards.
My guess is that the higher charges are damaging the bullets structurally which is causing the large groups and weird holes. This damage may be partially due to a rough factory barrel. Of course it's also partially due to the huge amount of powder and high velocities reached by the RUM case.
I do agree that a 1:9" twist is plenty of spin for these bullets, so the problem is not lack of stability. My hunch is that your rifle is just too hard on the bullets at very high speed.
There are two areas of bullet failure that might be possible (if it is a bullet failure problem). Either the exposed lead of the GameKing bullets is becoming deformed on firing. I've measured inconsistent BC's for lead tipped bullets as charge weight increases. I believe this is due to the lead tip deforming somewhat at greater accelerations. If this is the problem, you can solve it by going to any other non-lead tip hunting bullet.
The other failure that's possible is at the jacket. This would be due to a long bearing surface scraping down a rough factory bore at high velocity causing rips/splits in the jacket. If this is the problem, you can solve the problem by sticking to the heavier jacket options like the Nosler Accubond
. If this is a 'rough barrel' issue, I advise against the Bergers because their even thinner skinned than the Sierra GameKings.
Best of luck. Please let us know if you figure out what the problem is/was.