I have had my AK for about 4 months now. I have fired maybe 500 rounds. The other day I was at the range sighting in my mojo micro click sight. I was at the 50 yard rifle range and placing about 2-3 inch groups. After about 75 rounds my 2 inch group looked more like a 6 inch group. I know the barrel was getting hot. Is this normal? Does accuracy decrease with the barrel getting hot? I know I was gettting a little tired, but I thought for sure I was on mark.  Could the sight be loosing it's zero that quick? (It's a Global Trades AK from Houston) Thanks for any replies.

Can barrels be replaced on the AK? If so, can anyone recommend a good one?

Groups will open up as the barrel gets hot because of shot stringing and heat waves off the metal changing your sight picture. Also your eyes can get tired.

What kind of AK do you have? I doubt that changing the barrel will fix the problem.

What you can do is get your action cryo'd to elliiminate the stringing. You can also spray a substance on the top of the barrle to smother the heat wave effect or use optics.

As metal gets hot it expands.  This will usually decrease accuracy.  Although some barrels actually get more accurate as they get hot.

You didn't say if the barrel was clean or dirty when you started shooting.  Clean barrels are usually more accurate than dirty ones.

It could also be just dumb luck.  Sometimes an inaccurate gun/load combination will throw three shots in a row close to each over.  When the next shots open the group up, you realize it was just random chance.

As far as replacing the barrel on an AK, I'm sure it can be done.  But despite the occasional BS claim of near MOA accuracy, AK's are not accurate rifles.

AK accuracy is an oxymoron

I shoot about 6-8" at 100 yards with my romy, sustaine fire. And any gun I own, the accuracy goes down a little with heat.

So far my SKS has been as accurate as I am.

I think if I did my part with it I could get 1 inch groups at 50 yards. Granted, this is an SKS and 50 yards, but still good for any sort of cheap, mass produced commie weapon.

You should definatly be getting better groups than that 75 yards.

Try shooting someone elses rifle (not an AK, but with iron sights) at that range and see if you do better. This will tell you if it might be the gun/ammo or not.

Go back and try again. Practice is the best thing you can do to increase accuracy.

A "mil-spec" AK should shoot anywhere from 2 to 5 MOA on average. While 5 MOA isn't desirable, it isn't uncommon or unheard of. The action of the AK is very violent and it causes some "whip" or "flex" in the barrel, even when its cold and this degrades accuracy. As the barrel heats up, this is exacerbated and accruacy suffers accordingly. Barrel heat could explain your accuracy degredation. AK's don't really loose thier "zero". AK's don't have windage adjustible rear-sights, windage can only be changed from the front sight. The front sight is usually very stiff and doesn't like to be moved with the special vice-like tool, let alone recoil. Its possible the rear-sight could have loosened because of recoil, which would also degrade accuracy. If you were firing rapidly, the barrel would heat up and recoil forces would be excessive enough to loosen up the

sight. AK's typically have some "play" in the rear sight and this can be exacerbated by recoil forces over time, but this usually isn't an issue and can be fixed if desired. Replacing a barrel on an AK is much more involved than replacing a barrel on an AR. Adding a heavier barrel would reduce the the barrel "flex" and decrease the effect of heat on accuracy. It wouldn't be difficult to locate an HBAR for an AK, but installing it would be a pain. Personally, I don't think it would be worth the time. AK's are not "match" weapons, they are minute-of-asshole, and even at 6 MOA your weapon is capable of "defensive" accuracy. There was nothing done to mitigate the effects of heat on the AK at the design level in an attempt to discourage soldiers from wasting ammunition.
Another possiblity is bad/different ammunition, though you didn't really elaborate on this. My opinion is that everything seems normal....I believe your AK heated up from firing and your groups swelled accoridngly.