As stated, you don't need a riser or anything else. You won't even really notice the front sight post when you look through the scope.
If you start adding risers and stuff there will be multiple issues. You won't be able to get a good consistent cheek weld. Also, the higher the scope is, the more of an offset you need for closer in shots. If the center your scope is several inches above the bore, then your zero is going to be all wonky.
As for the 2 rings vs 1 piece mount, both have their benefits, provided they are made by a quality manufacturer.
It is possible to mess a scope up with either if installed incorrectly.
Another option is a riser. I know you don't want too many "moving" parts, but mounted correctly, the riser won't move at all. Some are high enough to be able to see through the channel and use your irons without removing your optics. Here's a link to several: https://www.google.com/search?q=ar15...ient=firefox-a. I recently went through this exercise with my Sig. I have a red dot mounted on mine and decided to chuck the riser because it wasn't high enough to use both sets of sights. Now I just cowitnessed my red dot to my irons and it's all good. If I ever chose a scope, I'd still have to decide irons or glass.
Just posted this in another thread but since more people are in this one I'll paste it here for help:
So I just got a Nikon P-223 BDC 600 for my rifle.
1) one dial adjusts magnification. What is the "eye piece adjustment" closest to the eye adjusting? is it focusing the reticle or focusing what i'm seeing thru the scope (i have only looked thru it in my living room so far)?
2) Nikon suggests you go to Nikon Spot On™ Ballistic Match Technology Program to see what distance each circle on the reticle means for a specified ammo. when i change the magnification between 3-9, the circles show different distances. i guess i didn't know the distance hashes/circles meant different distances once you change the zoom. seems like that's a TON of information to know when you're out in the field using the scope. is this correct?
1) It is called a fast focus eyepiece. You need to get outside to focus the scope. There will be instructions on how Nikon expects you to do this in the box.
2) The best way to measure drop is to shoot your own rifle at the distances you want to know. I shoot my hunting rifles out to 300 yds and measure the drop from my point of aim to the impact with a ruler. It's just that simple.
According the this link AR15 zeroing in at 50 yards is the most optimal up to 200 yards...
AR15 Zero: Introduction - YouTube