How much in the future is GGO supposed to be? AK-47 is an ancient weapon already but you can hardly watch news from great many conflict zones without seeing them in copious numbers. M16 is no different. Even forgetting that, gun designs are hardly random. I reckon most guns that stood the test of time were designed by professionals. It could be slightly challenging for game developers to compete with that and come up with many novel models that look as convincing. Pew pew laser guns are a different thing since they don't exist in reality and nobody thus expects them to look one way or another, other than to look futurisic.