Originally Posted by kalnaren
Accuracy is determined primarily by the bore and length of the barrel...
I'd say what affects accuracy most would be first the quality of your barrel and ammunition, then the stability of your hop up, and then the consistency of your muzzle velocity.
Google "is a longer barrel more accurate?" and you'll come up with a good number of results, most of which would indicate no.
As for realistic guns, I know you said no AKs, but doesn't Real Sword make their AEGs from de-milled Norinco recievers? Can't get more real than that.