Trijicon ACOG 3.5×35 BAC Riflescope – .223 / 5.56 BDC

The Trijicon ACOG BAC Riflescope in 3.5×35 with the Red Horseshoe BAC reticle and Target Reference System is the combat optic that defined a generation of American rifle shooting. The ranging reticle is calibrated for 5.56 and .223 caliber flat-top rifles out to 1000 meters, and the whole design is built to keep both eyes open and the shooter aware of everything around the target.

BAC stands for Bindon Aiming Concept, and it is the trick that makes a magnified optic behave like a red dot at close range. With both eyes open, the brain favors the illuminated reticle when the rifle is moving and the magnified image when it settles.

What the Trijicon ACOG BAC Riflescope Delivers

Illumination without batteries is the headline. Daytime illumination is provided by fiber optics that gather ambient light, so the reticle gets brighter as conditions get brighter. At night, tritium illuminates the scope, meaning the sight is always on with nothing to switch, nothing to charge, and nothing to fail at the wrong moment.

That makes this optic a natural for duty rifles, defensive carbines, and anyone who wants a sight that is simply always ready. The 3.5x magnification is enough to identify and engage at distance while remaining fast up close thanks to BAC. The Red Horseshoe reticle gives a fast close-range aiming reference with a fine center point for precision, and the Target Reference System adds ranging stadia calibrated to the cartridge.

Key Features

• 3.5×35 magnification and objective sizing for a balance of speed and reach
• Red Horseshoe BAC reticle with Target Reference System for ranging and holdovers
• Ranging reticle calibrated for 5.56 and .223 caliber flat-top rifles to 1000 meters
• Fiber optic daytime illumination that adjusts automatically to ambient light
• Tritium illumination at night, with no batteries required at any time
• Legendary Trijicon durability in a sealed, rugged housing

Reticle, Calibration, and Specifications

The bullet drop compensation built into the reticle is calibrated for 5.56 and .223 flat-top rifles, which means the stadia below the horseshoe correspond to specific distances when the rifle is zeroed as intended. Verify your zero and confirm your holds on paper or steel at known distances, because barrel length and ammunition selection both shift the actual drop from the calibration model.

The Trijicon ACOG BAC Riflescope mounts to flat-top receivers, so a standard Picatinny upper is all you need. Keep the fiber optic on top unobstructed, since covering it with a hand, a cover, or tape is what kills reticle brightness in daylight. Tritium has a finite half-life measured in years, so night brightness slowly declines over a very long service window.

Practical Use, Care, and Compatibility

Learn the BAC technique deliberately. Shoot both eyes open, present the rifle aggressively, and let the illuminated horseshoe do the work at close range instead of hunting for a perfect sight picture. Shooters who fight the concept by squinting through the scope give up the speed advantage the optic was designed around.

Clean the lenses with a proper lens pen or microfiber cloth rather than a shirttail, and keep the fiber optic channel free of mud and debris. Check the mount screws periodically, and confirm zero after any hard knock or after removing and reinstalling the optic. Browse our optics collection for mounts, backup irons, and magnifier alternatives.

Mounting height is the one setup detail people get wrong. Run the optic in a mount that puts your eye behind the scope naturally with a proper cheek weld, and add backup irons that clear the housing so you have something to shoot with if the optic is damaged. A Trijicon ACOG BAC Riflescope set at the right height and the right length of pull feels like part of the rifle rather than an accessory bolted on top of it.

Decades of hard service have already proven this design. Ships direct to your door, no FFL required.