I just built my first ar, its a Dissipator with an A3 reciever. That is to say it has a 16" CAR barrell with the handguards and sight radius or the 20".


My Question, is should it have a rear sight for a 20" or for a 16"?
I know that most 20" have the rear elevation knob that is 8/3 and that the 16" have it at 6/3.

My real question is why the difference. Is the the barrell length or the distance between the sights.