There are many schools of thought on how to sight in a rifle. For some, a simple 100 yard zero is sufficient for all the shooting that they plan to do. Others learned from dad or grandpa to sight in a couple inches high at 100 yards to improve trajectory. While both these systems can undoubtedly kill deer, those seeking the utmost efficiency desire something a little bit more efficient. Fortunately, there is a system that can optimize trajectory for a given cartridge and loading: Maximum Point Blank Range.
The Basic Premise
The fundamental concept behind the maximum point blank range (MPBR) system is that big game animals have vitals around 8 inches in size or bigger. This means that unlike precision target shooters, hunters have a little bit of wiggle room for bullet drop. As long as the bullet stays within a couple inches of the line of sight the shot will still strike the vitals and kill the animal. This doesn’t matter if the bullet strikes high or low.
Just like throwing a football, bullets travel in an arc towards the target. This means that besides at very short ranges a bullet will be arcing above the line of sight out to our zero range where it will start to fall below. Similar to a football, if you want to throw the bullet farther you need to arc it higher. After establishing an acceptable margin of error, we can figure out what trajectory gives us the longest arc which doesn’t go above our acceptable margin for error.
Example
To illustrate this point, it helps to look at an example. Let’s take a look at a common deer hunting load for a bolt action hunting rifle like a Ruger American. For this example we will use the 150gr Remington CoreLokt out of a 30-06 Springfield. First let’s take a look at what our trajectory looks like if we just zero our rifle at 100 yards.
This shows us that around 191 yards the bullet begins to drop more than three inches. This is about where shooters need to begin to compensate for drop. This means that our “point and shoot” range is 0-191 yards.
Now, let’s see what happens if we zero at our maximum point blank range. Using an online calculator the optimal zero for this particular loading is 235 yards.
As we can see, the drop and 300 yards is now less than half. In fact, the bullet doesn’t drop more than three inches until 274 yards. This adds over 80 yards to our effective “point and shoot” range. Because the bullet never goes more than 3 inches above the line of sight as long as we hold at the centre of the vitals, we will be accurate enough to cleanly kill a deer.
Sighting in with Maximum Point Blank Range
In order to use this type of system on your hunting rifle, you will need to do some number crunching with online calculators. Shooters Calculator is a great website that can take the particulars of your cartridge and tell you what your MPBR is as well as how high you will need to sight in at 100 yards. For example, in our 30-06 example we need to sight in about 2.7 inches high at 100 yards. Once you’ve figured that out it is as simple as going to the range and sighting in like usual.
Factors Increasing Maximum Point Blank Range
Using MPBR let’s you find the most efficient sight in distance for a given cartridge. However, once you start using this system you will quickly realize that some cartridges have much larger effective ranges than others. This boils down to two factors: velocity and ballistic coefficient.
First of all, velocity has an enormous effect on maximum point blank range. Calling back to high school physics, gravity acts as a constant. This means that gravity will pulls the same on fast and slow bullets. However, fast bullets get to the target quicker, giving gravity less time to work. This is why faster cartridges drop less than slower ones.
The second factor affecting MPBR is ballistic coefficient. Longer sleeker bullets cut through the air more efficiently and lose velocity less than less efficient. However be aware that high BC bullets tend to be heavier, and therefore tend to start out slower. It is important to run the numbers to know if the gained efficiency is worth the initial drop in velocity.
Closing Thoughts
The cartridges with the highest MPRB are going to be high BC fast travelling bullets. Cartridges like the 6.5-300 Weatherby Magnum can push maximum point blank ranges out to almost 350 yards. However, it is important to keep in mind that there are many reasons to pick a cartridge besides how far it can shoot. Recoil, front surface area, action length, and bullet selection are all valid concerns in addition to MPBR.
As such, considering all of these many factors are important when selecting a cartridge. MPBR is best used as a tool to get the most out of the cartridge you have, not as a metric for selecting which cartridge you will purchase. That said, MPBR is a useful tool to eke the most out of your firearm as well as understand it’s limitations.