Went and shot some today.
Shot some intentionally bent rounds with a pretty major wobble, single loaded w/o a mag. Saw no major fliers. 2-3" groups.
Then shot a few groups out of 10rds mags and saw the typical low flier on the last shot.
I examined the flash hider. It appeared not to be perferctly lined up with the barrel center line. Then saw a clear bullet impact (copper) streak on the top inside of the flash hider. I should have take a pic of this but lighting was poor. I believe this is the cause of the major low fliers.
Not sure if the mags had anything to do with this or not. I had purchased the 10rds mags after I rebarreled the rifle. The splines on this criterion barrel allow some play on the flash hider. Unless the castle nut is tight, the set screw can tilt the flash hider down - contact with the bullet - low fliers.
I have no idea still why the fliers seem to happen on last shots from mag.
I had the flas hider bored out to about .365 and then re-installed it carefully and checked alignment.
Back to the range for a quick re-test in fading daylight:
No fliers with reloads. The high misses are my fault - holding sight picture for too long, getting on the black.
The GG Nato still had what I thought were two fliers, both were the last shot out of a mag. Not sure what to make of this.
Anyway, I believe the flash hider misalignment was the cause of the major low fliers. Why it always seemed to happen on the 4th or 5th shot - no idea? Barrel heating up? Something determined whether the bullet made contach w the flash hider or not.
Anyway. The two 10-rd groups with my match loads are about what I would expect.
I will be ordering more CMI mags.