3-9x40 Tactical AO Scope - Open Box

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$39.99 - $49.99


It means this product has passed our rigorous 21 point inspection checklist and has been certified as renewed by the Monstrum Quality Control.

Monstrum Open Box Clearance products come with a 30 day money back guarantee and a 1 year warranty. 



Like-New - No sign of wear, everything included.

Blemished - Signs of wear, no signs of electronic, mechanical, or optical defects, everything included.


Types of Blemish Explained: Signs of scope being previously mounted (most common), scratches that do not penetrate finish (moderately common), scratches that penetrate finish (less common - any scratch that penetrates finish and exceeds 2" is not sold), signs of usage on prism turret housing (moderately common).


Any scope that has a scratch that penetrates the finish (aluminum exposure visible) that exceeds 2", any dents, or any gouges are destroyed and not resold.


  • Includes: S3940-AO-B Rifle Scope, Offset Scope Mount, Lens Cloth, Lens Cover
  • Reticle: Crosshair Reticle
  • Materials: 6061 Aircraft Grade Aluminum
  • Compatibility: Rifles with Picatinny Rails.
  • Scope Range: Close to Mid Range, 500+ Yards.
  • Magnification: 3-9x
  • Objective Diameter: 40 mm
  • Tube Size: 1 in
  • Eye Relief: 3.5-3.8 in
  • Weight: 14 oz
  • Length: 14 in
  • Color: Black or Flat Dark Earth
  • Fog & Water Resistant? Yes (Nitrogen Sealed)
  • Warranty: 1 Year Warranty
  • Download Product Manual

A new line of rifle scopes for shooters that want reliable optic without the bells and whistles (or the costs that come with them). The Monstrum Tactical S3940-AO is a full-featured scope suitable for hunting, target shooting, or tactical use. The S3940-AO weighs 1 lb 2 ounces. It has a 1 inch diameter tube and requires a mount with 1 inch diameter scope rings. The scope is 14 inches in total length. The outside diameter of the eyepiece is 44mm and the outside diameter of the objective lens is 50 mm. he S3940-AO includes a one-piece machined aluminum offset scope mount for mounting to Picatinny rail equipped rifles. The mount provides 2 inches of forward extension allowing for for optimum eye relief and shooting position.

What is Parrallax?

In terms of shooting, parallax refers to the alignment of the shooter’s eye in relation to the scope reticle and the target object. Unless properly focused, a shift in eye position will result in a shift in the position of the reticle relative to the target - the parallax effect. With a fixed objective lens scope (without AO), small shifts in eye position may result in imprecise targeting and less accurate shooting.

What is AO?
AO stands for adjustable objective (sometimes referred to as parallax adjustment).  An AO scope allows you to adjust the objective lens of the scope, bringing the target image into focus with the plane of the reticle.  When in focus with the plane of the reticle, the parallax effect is eliminated.  An AO scope allows you to 1) bring your targets into sharper focus 2) eliminate parallax and 3) gather ranging information about your target.


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