Anschutz and Remington 700 are regarded to be most accurate rifles in the world. NOMAN
Custom built
From a benchrest.
Impossible to answer as asked. Rifle, pistol, shotgun? What does accurate mean to you?
It is often accepted the Heckler and Koch PSG-1 is the most accurate sniper rifle in the world.
You have to work up the most accurate load for your particular rifle. Each rifle will respond differently to changes in bullets, powder charge, seating depth, etc. What is an accurate load in one rifle may shoot poorly in another and vice versa.
Too broad to answer. At what range? Rifle, rimfire, pistol, revolver? In general, a heavy barreled target rifle (most are custom builds) in one of the 6mm target calibers would be the most accurate to about 600 yards, but other rifles such as the .338 Lapua will be more accurate at 1500 yards.
Impossible to answer as asked. Factory or custom?
You will have to define "sniper rifle". There is no meaning to that term, other than an accurate scope mounted rifle. That includes most hunting rifles.
Generally, a telescopic one. Like a scope on a Sniper rifle
the rifle
The M16 is an assault rifle that is a .223 caliber / 5.56 mm. like any weapon it is only as accurate as its shooter, <><><> It can be very accurate.