So after years of salivating over mak90's, I bought a used one.  It showed no corrosion and the numbers are matching.

As usual, my bad luck is that it appears to be a lemon!  I tried a five shot group at about forty yards. My first shot was on the 2' X 2' target 4-5 inches below the bullseye.  For the next four shots, one was 12 inches off low and left, one was 8inches off to the right and the othe two were off paper!?!?

I've never shot any rifle that is so wildly inaccurate.

The rifle has a smooth trigger so the shots were not jerked off target.  I immediately got another AK out of my quiver and used the same ammo (monarch) to put a quick 5 shots into a five inch circle. It's not the ammo.

I verified the front and rear sight are not loose on the mak90.

Soooo.  What would you pros do?  

I assume it's the barrel or muzzle crown or possibly the chamber.  It would take a lot to wear out a barrel or chamber, but a muzzle crown could be damaged more easily.  

Of course I'm kicking myself for buying used.  A few hundred dollars more would have bought me a NIB version.  

Is this a one in a million, or are lemons a common occurrence in the mak90 game?

Sounds like you bought Bubba's problems.  My MAKs are among the most accurate AK's I have.  Check the crown area for nicks/gouges.  Does it feed, fire and eject OK?

Thanks for your reply.

Yes, feeds, fires, ejects with no problem.  I'm going to get a magnifying glass and examine the muzzle crown and see if I can see any damage.  

I thought these rifles were indestructible and therefore a used mak90 was a safe bet.  WRONG!

What would it take to damage the muzzle crown?  Poking a gravel road with the barrel?

How many rounds would it take to wear out a mak90 barrel?  10-20-30 thousand rounds?

But yeah, I did probably "inherit" bubba's problems.

Try a different brand of ammo.  I don't remember where, but I read an article about some AK's being a little different on the barrel diameter.  Want to say couple  thousandth's difference?

Don't remember which ones and maybe someone more knowledgeable can chime in.

Thanks for your input.  I'll try some different ammo and report back.

Ok, Southernshooter, hats off to you.  You are right and I was wrong.  Apparently it was the ammo.

I tried some Remington UMC and my newly acquired, used mak90 shot acceptably.

I have some other steel cased Wolf ammo to try in next outing.

I've looked at the muzzle crown with a magnifying glass and don't see any nicks or gouges that stand out

It was my fault to use such a small trial with the Monarch, but I have used it with several other rifles without problem.  Maybe it was a bad box of the stuff.  Hell, maybe it was me.   I was busy, short on time, and maybe wasn't focused.  Maybe I jumped to the wrong conclusion when it (I)missed such a large target at such close range.  In future I will do much more testing before jumping to conclusions.

Thanks for your help.

Refreshing to hear someone with an issue take advice and the REPORT BACK in timely fashion with the results!
MAKs are generally top-quality stuff That rife will probably outlast you (or the rest of us)

I've had mine for about 25 yrs and still love it as in day 1. I even threaded the barrel myself. Very accurate rifle.