Nightforce F1 ATACR and Defensive Edge Scope Level

Defensive Edge Scope Level: Review

The Defensive Edge scope level, also branded and sold by Nightforce Optics is one piece of long range shooting gear I’ve recommended a lot over the last several years.

The Defensive Edge scope level, or Anti-Cant Device (ACD) was developed by DE as a way to integrate a scope leveling device into the scope mounting system, rather than bolting on a tube-mounted level fore or aft of the rear scope ring.

Nightforce NXS with ACIACD

Designed to fit any Nightforce ring set, Direct Mount, or Unimount, it also works with Defensive Edge’s custom ring/base sets.

The difference between the Nightforce-branded level and the Defensive Edge scope level is solely in the finish. It’s also available as a combination ACI/ACD mount. The Angle Cosine Indicator (ACI) is used to determine the cosine of the angle to the target. Largely abandoned now in favor of devices with inclinometers built into them, the ACI used to be a staple item on a long range precision rifle. It’s still available if you want one.

Nightforce NXS with Defensive Edge Scope Level and ACI Mount

The beauty of the design lies in its simplicity.

It’s a piece of precision machined aluminum with a simple bubble level secured to the top of it. It can be used by right-handed shooters, as well as those who mount the scope with their left eye. It can be seen while on target and easily checked by a spotter on either side of the shooter. It’s very easy to install and adjust—remove the existing rear cap, level the reticle, then install the scope level by alternating tension on the screws until the level is torqued properly and indexed on the plumb reticle. Once this is done, you can remove the scope and rings as a single unit and move them to another rail without adjusting the level because it’s indexed to the reticle rather than the rail.


Defensive Edge ACD / Nightforce UL Rings

Defensive Edge ACD with Nightforce Ultralight rings

The only drawback to the Defensive Edge scope level is it only works with Nightforce products and Defensive Edge mounts.

I don’t consider that a drawback as they are the only rings and mounts I recommend anyway. My standard mounting system is the Nightforce 40 MOA steel rail, Nightforce Ultralight rings, and a Defensive Edge scope level. They are rock-solid and just plain work. Try them out for yourself.

For ordering information, visit or any Nightforce Optics retailer.

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As an Idaho native, avid hunter, and long range shooter, Sam has written numerous articles and gear reviews for various online publications. Specializing in long range hunting in the mountains of northern Idaho, Sam founded Panhandle Precision as a way to continue sharing his passions.

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  • Luke Guidry
    December 3, 2016 at 18:34

    Would you say running the 6 screw mounts vs the 4 screw mounts a huge plus? asking because i want to install the level/aci top mount combo and I’m curious if the 6 screw option would offer anything more than the 4 screws I’m running currently.

    • Sam
      Sam Millard
      December 3, 2016 at 20:04

      This rifle is the only one of mine that has the 6-screw rings. All of my other ones, including the 338 Edge +P wear 4-screw rings. I suppose a 6-screw mount theoretically has more clamping area, but I imagine it would be hard to prove whether or not it’s a huge advantage.


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