This was a good read by Patrick E Kelly...
Just because a gunwriter, the military or some tactical guy on TV stipulates a 300-yard zero does not mean you have to follow suit. What if you’re only going to shoot at 100 yards?
Depending on the ammunition, your trajectory can vary a great deal, showing extreme variations in point of impact (POI) in relation to point of aim (POA) at longer ranges. If you plan on employing your AR as a battle rifle, the Maximum Point Blank Range (MPBR) method has merit. The premise is being able to hold on your target over the longest distance possible and still get hits. MPBR depends primarily on two things; target size and trajectory.
For example, the Black Hills 69-grain Sierra MatchKing load produces 2,702 fps from my Del-Ton AR with a 16-inch barrel. If I specify an 8-inch target, my Sierra Infinity ballistics program tells me the MPBR for that load, at that velocity, is 296 yards. This means the bullet should not rise or fall above or below the line of sight (LOS) more than 4 inches from the muzzle out to 296 yards.
Switch to the Hornady 40-grain V-Max with a velocity of 3,342 fps and the MPBR changes to 330 yards. What’s interesting is, to achieve a MPBR zero for the 69-grain load, I’d zero at 33 yards. For the 40-grain V-Max, I’d zero at 39 yards. Experience has shown that sighting-in somewhere between 30 and 40 yards will generally produce a MPBR for an 8-inch target with most .223 Rem. loads from an AR.
The problem with an 8-inch target MPBR zero is your rifle will be shooting about 3 inches high at 100 yards. If that’s OK and you can hold to make the correction, no worries. If you want your 100-yard POA/POI to be the same, zero at 100 yards. Just remember, if you zero at 100 yards, you’ll be a foot or more low at 300 yards, depending on your ammunition of course.
AR carbines are often employed at very close range. If you’re keeping one for home defense, you need to be able to deliver accurate fire up close. Because the sights are about 2.5 inches above the bore, your bullet will strike about 2 inches below your POA inside of 10 yards. If you are trying to shoot a werewolf in the head across your living room, this could get tricky.
In multigun, the choice of rifles is the AR-15 or one of its derivatives. With that said, the rifle of reference for the balance of this article is an iron- sighted, 20-inch-barreled AR-15.
To be effective in the ever-changing game of practical shooting, you must have intimate knowledge of your bullet’s trajectory. Since long-distance targets present a small aiming area, a 6-o’clock hold is generally preferred. This allows the shooter to have a good visual hold point without having to look at the target to maintain the hold. My primary zero has the point of impact at the tip of the front sight at
300 yards. This gives me a 6-o’clock hold for all targets between 75 and 240 yards. From 240 to 320 yards, I only need to have my front sight on target at the break of the shot. I have this zero information written in clicks as come-ups from the rear sight at its lowest (bottomed) position.
Beyond your primary, you should have additional range-proven zeros as reference tools for other target presentations. Targets approaching 400 yards or farther will require their own zeros. A rifle zeroed for a bullet point of impact (POI) at 450 yards will have you shooting over targets from 125 to 375 yards, as the bullet’s trajectory is well above your 6-o’clock hold. This makes the job of holding where you want to on those mid-range targets more difficult.
Having multiple zeros on hand gives you the flexibility to approach a course of fire in a manner that best suits you. At the 2010 JP Rocky Mountain 3-Gun Match held at the NRA Whittington Center, I employed several different zeros. Over the*three days of competition I “clicked-in” different zeros, depending on target presentation and distance, and even clicked between target arrays on one stage. Instead of trying to hold well below the close-range targets with a zero that would improve my ability to hit the 400- and 500-yard targets, I broke the target array down into near and far and clicked between them, all while on the clock. It worked well enough that I was able to pick up my third win.
