Fenix Ammunition: Maximum Point-Blank Range (MPBR) – The Best Rifle Zero For Your Home Defense Carbine?

Maximum Point-Blank Range (MPBR): The Best Rifle Zero For Home Defense?
Often, the question is asked: what is the best way to zero a rifle for short range work?
For a long time, conventional wisdom has suggested that the 50 / 200 yard zero is the most useful for the modern AR-15 rifle as the 5.56x45mm cartridge remains relatively flat across this distance.  While this is true in some cases, this thought process is a ‘catch-all’ generalization that does not factor in barrel length, cartridge type, projectile weight, optic style, and many other factors that make each carbine unique to the user operating the weapon system.  Due to the massive popularity of the AR-15 platform is it highly likely that YOUR setup is not the same as the ‘vanilla standard’ rifle used to develop the 50 / 200 method.  So, what do we do?
Enter Maximum Point-Blank Range, or MPBR.  MPBR is not a set standard of range, but rather a methodology used to determine a single ‘hold’ which will allow the operator to make hits on target all the way from the muzzle out to the end of the rifle’s point-blank range.  Point Blank Range is the range at which you don’t need to ‘aim high’ or ‘aim low’ in order to hit your target.  Remembering that when you fire a bullet our of your rifle, the bullet rises and then falls through your line of sight because the rifle optic is higher than the centerline of the barrel.  This means your reticle could be covering exactly where you want to hit the target, but the actual point of impact will be either higher or lower than the reticle depending on the distance.  Therefore, MAXIMUM Point-Blank Range is the farthest distance one can expect to hit their target while maintaining a ‘dead hold’ on the center of the target.  The illustration below helps shed light on what’s happening here:

So, why is this method useful?  Because time is important!  Whether you’re in a 3-gun competition, a defensive scenario, or out hunting, it is likely the target will only present itself for a very short timeframe and it’s likely you will NOT know the exact distance to the target.  Ranging and doping your target, even using a Bullet Drop Compensating (BDC) reticle, presents the opportunity for wasted time and miscalculation.  When the target shows, we want to be putting rounds downrange as quickly as possible with the highest probability of intersecting our target, WITHOUT having to estimate range.  Anything within the Maximum Point-Blank Range should be able to be hit without adjusting hold over, hold under, or BDC stadia.
Sounds great, right?  So, why aren’t more people using this method?  Simply put: it takes a little bit of math and a couple assumptions about what we’re trying to accomplish.  Let’s start by examining the variables at play.
Bringing this concept into reality for a moment, the average human face presents as an oval target approximately 6 inches in width and 9-12 inches in height and a standard IPSC/IDPA size target consists of a 6-inch square ‘head’ and an 8-inch perforated circle in the center of the thoracic cavity.  Therefore, it is logical to use a six-inch diameter circle, or a 6-inch vertical ‘resolution’, as the first defined constant in our equation.
Once the desired vertical resolution is defined, it is necessary to determine the ballistic trajectory of the projectile exiting our carbine.  This requires the following variables to be defined:

• Projectile weight
• Projectile muzzle velocity
• Height of our optic above the barrel

As you can see, the MPBR method is going to ‘tune’ our zero to our exact combination.  Muzzle velocity is of course dependent upon our barrel length and the powder charge of our ammunition, so let’s look at a few common combinations so we can begin to see how the details might come together:
 
5.56x45mm 55gr XM193                               .300 Blackout 110gr V-Max        
Barrel Length     Muzzle Velocity                Barrel Length     Muzzle Velocity
9″                           2,591                                     9″                           2,116
10″                        2,689                                     10″                        2,173
14″                        2,978                                     14″                        2,337
16″                        3,083                                     16″                        2,397
18″                        3,172                                     18″                        2,448
 
Using a 16” barrel and shooting XM193, our muzzle velocity is 3,083 feet per second and our projectile weight is 55 grains.  Please note: the above data was obtained in a test rifle during average atmospheric conditions, and MAY NOT be accurate for your rifle.  For example, if you are using 62 grain ammunition and a shorter barrel length, you will need to verify your actual muzzle velocity over a chronograph to establish these variables.  Temperature and barometric pressure will also play a role, but for the purposes of this discussion we’re assuming average indoor conditions – exactly what would be expected in a defensive or CQB situation.
The next step requires a ballistic calculator, of which there are many options on the internet and numerous smartphone-based applications that can be downloaded.  This will allow us to calculate the distance at which the projectile will have fallen 3 inches below our line of sight, or the point at which the projectile will impact the target at the BOTTOM of a 6-inch circle assuming the optic reticle was held at the center of the circle.  This requires us to measure the height of our optic above the centerline of the barrel; in this example we’re use an EoTech EXPS3 which has a 2.60-inch height from the center of the red dot to the center of the barrel on a standard flattop AR-15 rifle.
From here we will do a bit of ‘plug and chug’, as most ballistic calculators use distance as the constant variable to calculate bullet drop.  What WE want to do is use a 3-inch bullet drop as our constant in order to determine our Maximum Point-Blank Range distance; in this case, an MPBR of 283 yards using a zero of 245 yards.  We used
So, what does this tell us?  What’s with the odd numbers, and what are we supposed to do with this information?
The answer?
By setting our zero at 245 yards, we will be able to make hits on a 6” circle by using a dead center hold all the way from 0-283 yards.  No adjustments, no over or under holding, no doping or ranging necessary.  The table below helps illustrate the path of the projectile as it exits the barrel:
MPBR Using A Six Inch ‘Kill Zone”

Due to the height of the optic above the barrel, the projectile starts off lower than our point of aim for the first 45 yards or so.  It briefly crosses the reticle before rising ABOVE our point of aim for the next 200 yards before once again crossing our point of aim, then dropping below the point of aim and eventually falling to earth.  If our target is standing exactly 245 yards away, the projectile will impact exactly where the reticle was held.  At 150 yards, our projectile hits 3 inches HIGH, and if they happen to be standing 1 yard or 283 yards away, the projectile will impact 3” BELOW the reticle on a center hold.  This gives us the ability to hit a six-inch target from muzzle contact all the way out to 283 yards with a single, dead center hold.
For close quarters (CQB) environments, it may not be necessary to think about hitting targets out to 283 yards.  However, we can see that the same MPBR zero will give us hits between 2.53”-0.99” below the reticle out to 25 yards, which should be acceptable for most such encounters where quick reaction speed is more important than absolute precision. CQB encounters are typically won by the party who can hit their opponent’s thoracic or “T-Zone” first, emphasizing the importance of being able to point and shoot without spending brainpower estimating range.
A common size for body armor rifle plates is 10” wide x 12 tall”, which means the center of our reticle can be offset by as much as 7” higher or 3” lower than the center of the rectangle in order to strike the area which would be covered by the plate.  This is important for defensive scenarios because it is extremely unlikely that our target will actually be wearing body armor, and the whole point of body armor is to cover the areas of the body which are most vulnerable.  Stacking two or three rounds into the area which would otherwise be covered by a rifle plate virtually guarantees incapacitation provided we’re using proper ammunition.
From a competition perspective, it is rare to see a target smaller than six inches in diameter.  Most plate racks and popper targets have at least a six-inch circle, and many provide an eight- inch circle.  For those in production or tactical divisions that limit magnified optics, a single zero can provide quick shots at close range as well as simplicity for longer range targets especially if the distance is unknown.  The average human being can determine whether the target is within 283 yards through a quick glance, especially if they’re shooting an event at a range which they know is shorter than 283 yards in length.  It DOES NOT MATTER if the range is 100 yards long, or 200 yards long, or 250 yards long: the center hold will be all they need to hit the target.