I have one of the 4-12x40 redfield revolution scopes with the accu-range reticle on a flattop 16" barrel AR. It is a great scope. I dont have a whole lot of experience with scopes so I only have a couple other ones to compair it to. before i purchased it i read every thread i could find on line about these scopes. did not find any bad opinions of them. I have a fixed front sight and I cannot see it in the scope at all. Here is a link of a picture of a similar rifle to mine with the same scope and mount that I have. pretty cheap mount but has worked ok so far.
http://img522.imageshack.us/img522/720/photo010tf.jpg
here is the thread that the pic was posted in. they discuss mounts in the posts
http://www.calguns.net/calgunforum/archive/index.php/t-389104.html
I have a friend with the same scope in 3-9x40 on a 30-06 hunting rifle and he loves it.
hope this helps