36 Yard Zero

The 25m / 300m zero is a myth.

Your AR15 rifle can be zeroed at either 25m, or at 300m. But not both at the same time.

Now, The Rifleman can already hear the murmurs in the crowd...
"Well, you'll be close!"

Perhaps.

However, if by "close" you mean that you can zero at 25m, and be on paper at 300m, then The Rifleman has some bad news for you. It's not gonna happen. 

The best way to get a true 300m zero is to take your rifle to a range that goes out to 300m and zero it at actual distance. The next best way is to zero about 3.5" high at 100 yards. 

Or, you can zero on the money at 36 yards (33m). Don't believe The Rifleman?  Check this out!

Using an AR15 with a 16 inch barrel - arguably the most common AR barrel length in the United States - The Rifleman performed an evaluation. The rifle wore a Primary Arms 1-6x scope featuring the patented ACSS reticle. The scope has been zeroed at 100 yards, as per the instructions. Additionally, it has been verified at 300 yards. 

The Rifleman set up a target at 25m (27 yards), and put the 300 yard aiming point at the center of the target.  Here's the aiming reticle, and emphasis on the point used to aim:

The 300 yard aiming reticle was placed dead center on the target and a deliberate 5-shot group was fired. 

As you can see, the group was nearly a full inch low. 




Next, The Rifleman put up a target at 36 yards (33m). A careful 5-shot group was fired. 

As you can see, right on the money. 




Caveats -
* 300 yards is not 300 meters. 300 meters is closer to 328 yards.  A rifle zeroed at 300m and fired at 300 yards will have bullet impacts about 2.5" high - less than 1 MOA. A rifle zeroed at 300 yards and fired at 300m will see bullet impacts about 2.5" low - again, less than 1 MOA.

** The 36 yard zero will work with 55 grain M193 clone loads and 62 grain M855 clone loads. 

*** The 36 yard zero will work for 14.5" barrels. The bullet impact at 300 yards will be 3" low (1MOA).

**** The 36 yard zero will work in an 18" or 20" gun. The bullet will impact about 1" high at 300 yards. 

***** If at all possible, always verify the zero at actual distance. If you do not have access to 300, then fire at 100: the group should be about 3.5" high. 

This zero will see all bullet impacts within 5" (the size of a CD or DVD) all the way out to 300m. At 400, the bullet will strike 16" low (aim at brim of cap to strike center mass).