I'll be taking a Patrol Rifle Instructor Course (LEO) in July and will be using a Colt AR-15, CMP HBAR Match Rifle.

I've been reading up on zeroing the sights. The question I have is that the rear sight is not marked for 800 yards.......instead of the 8/3 marking, its marked 6/3 (which would mean 600 or 300 yards). Is this correct??

Also, to the right of the 6/3 looks like a small 2........continue turning and you get 4, then 5. Does the 2 represent the 200 yard mark? And if so, why would it be after the 6/3???

The small '2' is actually a small 'z' for zero.  It's the position of the rear sight for zeroing on the US Army 25meter BZO course.  After BZOing at 25m (with M855 62g ball) your rifle will be zeroed for 300m when you return the sight to 8/3.  I believe the 'z' is one click below 8/3 on a M16A2, and two clicks below 6/3 on a real M4.

Of course your rifle is civilian so the barrel length, twist, amount of shift per click, etc; may be different from the military standard, in that case you may have to do some experimentation (or research) to figure out exactly what works in your rifle.

Also remember that the increments on the military drum is specifically matched to the trajectory of M855 ammo in the military length 1/7 barrel.  If you shoot a different load the range indicators on the drum may not correspond as closely as you would expect.

the 2 is a z for zero , use it and the small arpeture to zero your rifle for elevation with the front sight and windage with the knob. then once it's zeroed turn the elevation knob back to the 6/3 mark , it should have a flat spot on the dial and use that for general shooting or turn it up to whatever range you are shooting at.

Well how about that......it is a "z".......darn eyes are getting old....gonna need some specs soon I guess.

Any idea why this rear sight has the 6/3 instead of the 8/3????

Because your elevation adjustments are 1/2 minute instead of 1 minute.  Therefor, the full turn of the wheel doesn't raise the sight as high.  Be happy[:D] Means you can get a finer zero, and make finer adjustments at longer ranges.