a quality AK is just as accurate as a quality AR15.. the reason you have this misconception that AKs are so inaccurate has a lot to do with a lot of people owning some pretty poorly put together AKs from places like century and the romanian AKs were never upper tier in quality either, nowhere near the quality of polish, east german, or bulgarian AKs
polish archer rifles (they are 5.56mm) will shoot as well and sometimes better than a standard configuration AR15 (im not going to include AR15s with match barrels, free float shrouds etc because then it wouldnt be a fair comparison as the archer shoots 1 MOA without all of that, so compare it to a similar equipped AR)
another reason AKs seem to be a lot less accurate when compared to other rifles is the fact that for the longest time the only choices youve had in ammunition has been old military surplus ammo where handloaded and match ammo for the AR15 has been around for a very long time.. so comparisons are usually done with quality factory or handloaded ammo in the AR15 and surplus in the AK.. again, not a fair comparison
this is all assuming using similar optics as well, not iron sights which would also yield better results for the AR15
this is why its nice to see the test results from the archer rifle, being a 5.56mm AK youre capable of using the same ammunition in each of them for an accurate comparison with fewer variables and yeah.. theres absolutely nothing about the AK design itself that makes it inaccurate, just low quality builds and bad ammo muddying up the test results
on another note, there are a number of people that have been able to achieve sub-MOA accuracy with saiga 308s using match ammo.. so an 800 yard rifle is well within the realm of possibility