AK is a good design, now the execution of it....
Basically, what we are talking about is a design with a gas piston long stroke above the barrel and rotating bolt lock. Now, if you look at SIG 556, what do you see? The SAME THING. If you look at VALMET, what do you see? The SAME THING. If you look at Galil, Beretta M70, etc, what do you see? The same thing.
The issue with accuracy comes from TWO sources:
1) How was it made. You can get an AK, especially Finish (Valmet), Russian or Yugo made, that will be VERY accurate to about 200meters. Then again you have hungarian and romanian ones, which are usually worse. it is an issue of tolerances and balance and QC.
2) Ammunition. People who critisize AK for bad accuracy forget that it is not the SYSTEM, it is the CARTRIGE. What was this rifle built for? As something more powerful then a PPSh, needed to arm mass of Motor Rifle Divisions (an equivalent to Panzergrenadeers). The issue was VOLUME OF FIRE and engagements at the ranges 300-400m. Replace the round, give it 2-3 more inches of barrel and then you will see a HUGE difference.
3) Nobody complained about bad accuracy in Galil 7.62NATO. And that is AK.
Why? BEtter cartrige, better built. Nobody is complaining about accuracy of Saiga .308 or .223. Change the cartrige and see the difference.
4) Yugo M76 sniper rilfe uses 7.92 Mauser cartrige in an AK style rifle. It has NO issues with accuracy.
The basic system, is the same system used on: FN FAL, Bereta M70, Valmet, Galil and bunch of other systems: rotating locking bolt with 2-4 lugs, gas tube ABOVE barrel and a gas piston with long stroke. This system was first tried in SVT-40 rifle, then copied in FN-FAL and many others. The problem is with 7.62x39 cartrige, more then anything. Replace it with 6.5grendell and you will see TOTALLY NEW ballistics.