Here is what this thread will come down to. 5 pages of AK guys saying that the 5.56 round is the best round ever developed for killing anything up to an including a T-Rex; while the 5.45 round is the most worthless round ever made and you would be better off with a single shot .22short CB cap, and it wouldn't hurt a chipmonk (because you know, chipmonks are people too
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The AK guys will tell you it is a very good round an works well for what it was designed to do. It is a flat shooting round that holds its effectiveness out to almost its max. range. It has less recoil than the 5.56 although is not quite as accurate due to the gun itself.
The Soviets may not be the most technological people in the world, but will change something very quickly if found not to be effective in the field. It has been in use since the mid 70's. if it was as bad as all the AR guys say, it would have been replaced long ago.
The best thing to do is to shoot an AK-47 varient, then a 74 varient. You will notice the difference right away.
As for this debate, it is like a 1000 drunk guys fighting over which is best, Chevy or Ford.