NightForce C637: ATACR 4-20x50mm F1, Tremor 3

Nightforce : C637
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New for 2021, the 4-20x50 F1 fills an important magnification range in the ATACR line. Equally at home atop a bolt action or a semi-automatic rifle, the 4-20x50 F1 is smaller and lighter than the 5-25x56 F1 while offering a 25% improvement in magnification over the 4-16x42 F1. With Digillum, a ZeroStop turret, power throw lever, ED lenses, and 20x max magnification, the ATACR 4-20x50 F1 is the apex mid-power scope.



  • Focal Plane: First
  • Objective outer diameter: 50mm
  • Exit pupil diameter - 4x:8.3mm 20x:2.5mm
  • Field of view @100 yards/100 meters - 4x: 23.6ft 20x: 6.9ft 4x: 7.9m 20x: 2.0 m
  • Eye relief: 90mm/3.5 in
  • Internal adjustment range (MOA/Mil) - e: 130 MOA w: 100 MOA e: 38 Mil w: 29 Mil
  • Click value - .250 MOA .1 Mil-rad
  • Parallax adjustment: 11 yds - ∞
  • Tube diameter: 34mm/1.34in
  • Eyepiece outer diameter: 45 mm
  • Overall length (inches/mm): 13.9
  • Weight (ounces/grams): 35.2 oz
  • Mounting length (inches/mm): 4.1 in
  • PTL (Power Throw Lever): Standard
  • Reticles available - MOAR™ MIL-C™ MIL-XT™  TReMoR3 *
  • Elevation Feature: ZeroStop



  U.S. Government Export Restriction

This item is restricted for export by ITAR. Make sure that you are familiar with all applicable laws.  ITAR Information.


  FNBNA Financing (This option is for orders of $2000 or more.) 

We offer financing through the First National Bank of Northern Arkansas. Financing Information.



Max Magnification:
Reticle Position:
First Focal Plane