Help me make the right desion

[camoman]

I am currently looking for the right scope to make my rifle effective to 500 yards or farther. I have an AR with a 20" match heavy barrel. Leupold mark AR 4-12X40MM
Millett Tactical 4-16x50mm
Nikon M-223 3-12x42mm
Pentax Lightseeker 4-16x50mm
Vortex Viper PST 4-16x50mm
Which of these scopes would be the best choice for my AR? Thank you all.

[fixit69]

Go for higher magnification. That's what i'd do, but my eyes suck! You have some decent choices, but go handle one and look through it. Don't just go by what the masses are buying. Go with what feels good to you.

[Failure2Stop]

"Effective to 500" leaves a lot to interpretation.
What size targets do you need to hit?
Under what conditions do you need to hit them?
What kind of experience/training do you have on optics?
What kind of experience/training do you have with long-range shooting?
What is your budget for optic and mount?

[camoman]

I am talking about hitting something the size a prairie dog at 4 to 5 hundred yards. I am not well trained with the use of scopes, or long range shooting. I am accustomed to working under pressure, and a quick learner, and will be training to become just as effective at long range as I am short range.

[NWPilgrim]

My experience is that glass quality, and ruggedness/reliability are more of a help than magnification and even objective lens diameter in reasonable light. 8x at 500 yds is like 1x at 63 yds. That is pretty good as a starting point. 12x at 500 yds is like 1x at 42 yds. 16x at 500 is same as 1x at 31 yds.

Know what you want each feature for and then the decision is easier. Which one has the better glass and coatings? Do you need a 50mm objective lens for light gathering at the higher powers and don't mind the much bigger size and weight?

I don't know about the other models, but the Nikon Monarch series is excellent for glass quality and light transmission at this price point ($350?). In fact I am thinking of buying that exact scope for my new 20" AR15 for sighting in handloads and for 500-600 yds informal target shooting. I'm thinking that is the biggest scope I want on an AR, and even considering the Nikon M-223 in 2-8x.

I would ask fellow prairie dog shooters to see what works for those conditions.