The old eyes are getting tired , any suggestions on a varmint scope , probably in the 16x max power , will also be used off a bench. 18" Larue Stealth barrel .   $500 + mount,  price range give or take  if possible . Yotes out to about 200 yrds would be max shot yardage  

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rifle is ??  an AR15 chambered in ???
Distance to  (coyote) fast moving target 200 yds or less.
When you say Varmit scope I think prairie dogs there is a big difference in the correct optic to take the head off a prairie dog at 300 to 400 yds and the scope that is right to smoke a coyote at 200 yds and under.
For a Coyote I would recommend a Trijicon ACOG  3x or 2x is plenty because anything that moves fast you need a wider field of view to get onto the target.  A 1-4 Accupoint with a red post would be a fine choice. A 3-9 Accupoint would work but the 2.5 to 10 has a  56mm objective and is a lot brighter plus there is a big difference between 2.5x and 3x  you wouldn't expect that but there is.  Trijicon makes a compact ACOG 1.5x and 2x and a 3x with a  red illuminated crosshair which is really a nice optic for an AR because it is small and handles well.  The La Rue RCO Mount  is the best choice for that.  Yes you could get away with an optic that is 4-16 or 5-20 if you plan to spend time punching paper and want to see the holes but those big heavy scopes are exactly that big and heavy and on a light weight rifle not really the best choice.  Now if you were running a White Oak Armory 26 in heavy barrel then by all means drop a Nightforce or US Optics scope on that big boy and smoke those prairie dogs.

I have a nikon black fx 6-24 on my 204..  I've been very happy with it

My bad 556 , thanks for the info , was just looking at Larues optic and mount options

With a $500 price range you're looking at Lower mid range optics.  Vortex Viper HS or HS-T.  I have a 2-10 HS and a 4-16 HS-T and they work pretty good.  

Honestly on a 223/5.56 you wouldn't really need 16 power for hunting since the round really doesn't hit very hard out past 400yds if you're shooting Coyote.  I have shot many yodel dogs with the cartridge and once you get much past 300yds you will see spinners and runners far more than when shooting 204Ruger, 22-250, or 220 Swift etc.  I rarely use more than 6 power when coyote hunting.

If you're looking to shoot something like ground squirrels then I could see the higher magnification coming in handy.  I have a 20 power that I use on my rifle for prairie dogs.  

Used SWFA SS 3-15x42 in the EE. FFP mil reticle. Used to see those regularly at $500-$550 usually with mount in the EE. Have not been following the EE for a little while though.

Only potential negative is the FFP reticle covering a small target at long range. The 15x reticle is not near as thick as it is on 20x on the 5-20, but not as fine as a second focal plane option.

Midway has the Crimston Trace 3 and 5 series scopes on sale.  They're made in Japan by Light Optical Works, same company that makes the Nightforce scopes.  Think of them as a stripped down Nightforce.  I have one on my Savage 12 LRP and really like it.

$449 for one and it's a damn good deal.  Normally they're $1,200 and above.

https://www.midwayusa.com/product/1020619264?pid=133422

Thanks for the suggestions guys

NF NX8 2.5-20x50