As an update to this thread, I did get some match grade ammo (Privi, 75gr) and put 20 rounds through this rifle. I know that 75 gr is perhaps a bit on the high side for a 1:9 twist, but it's all I had access to...and they were all punching round holes in the target, so I assume there were no stability problems with them.
The bottom line is that thing MAY have tightened up a little but not a significant amount (still 2" - 3" at 100yds).
I took a look at the barrel and crown and I'm hoping I found the problem. I posted in a separate thread here:
How bad is this crown?
Have a look and share your thoughts.