I had a similar issue with my Accurav2 when I was first shooting it. After the first shot or two with Power belts, I couldn't get the bullet seated all the way down, and the groups were inconsistent, around that 6"-9" mark you're seeing. It was my first time shooting an inline, so I wasn't paying close enough attention. I switched to Hornady SSTs and I could always get them all the way down, without a good brushing, and the gun is a tack driver.
You could always trying a quick brushing between shots to see if that helps. With white hots, I was getting crud ring close to the breech plug, and I needed to make sure that's where the brushing happened.
If you have a Chronograph or radar, you could verify consistent velocities too. That might tell you something related to seating.