My Saiga variant started keyholing. Tier One finally diagnosed it as a brake issue after a new brake was put on and the old one could be carefully inspected. By Process of elimination,  ammo switched ,  barrel inspection indicated barrel was ok.  So, what else could it be---the brake. Turns out the pinned but non welded brake was moving all so slightly, probably thousands of an inch when the rifle was being fired, just enough to effect bullet spin. Put on a brake recommended by AKOU and sold by them--BD2, (great brake and good price)- Tier One pinned and welded the new brake.  Problem solved. If you rifle develops keyholding, go through the steps before you spend the $ for a rebarrel. Sometimes a non welded pin can start to walk out and you might not even realize it. 

If the brake was moving, you would be able to feel it. Id be more curious about the concentricity of the brake which can be a little tricky on AK's.

2 hours ago, Shane45 said:

If the brake was moving, you would be able to feel it. Id be more curious about the concentricity of the brake which can be a little tricky on AK's.

This!  

3 hours ago, Maksim said:

This!  

Didn't realize it but the fit was a problem, the pin had loosened and the brake did have movement to it.

Just now, SJG said:

Didn't realize it but the fit was a problem, the pin had loosened and the brake did have movement to it.

Glad you got it resolved! 

I see. If it was moving, I could see it messing with harmonics, but I would have theorised that would have resulted in a grouping issue, not actual keyholing. There was no jacket "smear" inside the brake? Hope you dont mind my questions. Topic is interesting to me.