The best thing about magnum cartridges is you can shoot farther and hit your target without knowing precise range. Magnums maximize a sighting system know as Maximum Point Blank Range. It’s the fastest, surest way of making hits on game animals without needing a rangefinder, ballistic calculator, ballistic reticles or dialing turrets. If you like fast and simple, learn MPBR and get a magnum.
MPBR is the farthest any particular rifle/cartridge/bullet set-up can shoot while keeping the bullet within the vital zone of your target. This distance increases with size of the target, and you can adjust your zero to maximize it.
The easiest way to understand the concept is to imagine shooting down a long, straight pipe that extends from your muzzle to the target. Zero your rifle so bullets just miss kissing the inside top of the pipe at their maximum trajectory. Then, when they fall to strike the bottom of the pipe, that is your MPBR, the farthest you can hold dead-center and expect to hit your target.
Let’s make the target a deer with a 10-inch vital zone on its chest. In reality, this vital zone is slightly bigger on a mature buck, bigger yet on an elk and absolutely huge on a moose, but much smaller on a coyote and smaller yet on a ground squirrel. So, the larger your target, the longer your potential MPBR with any bullet. For this exercise, we’ll compare a .30-06 to a .300 Rem. Ultra Mag. (RUM), shooting a 180-grain spire point with a B.C. of .500. The .30-06 throws this bullet at 2,800 fps, while the RUM spits it at 3,250 fps.
Our first task is to set the scope on each rifle so that our bullets won’t quite strike the top of the imaginary pipe, which is 5 inches above Point-Of-Aim (POA). I’ll cheat and use a ballistic calculator. If I zero at 288 yards, I’ll be 4 inches high at 100, peaking at 4.95 inches high at 160, then gradually dropping until 5 inches below POA at 340 yards. MPBR for this bullet/load is then 340 yards. I can aim dead center on a target 10 inches in diameter and expect to hit the 10-inch target (if air density remains constant, shot-to-shot velocity doesn’t vary significantly, I don’t flinch, pull the shot, etc.).
With the RUM at 3,250 fps, I can zero for 332 yards. Trajectory peaks 5 inches high at 180 yards, falls 5 inches below POA at 393 yards, making MPBR for this magnum 53 yards longer than for the .30-06.
An elk’s chest is 24 inches, top to bottom, so we can be conservative and allow a 16-inch vital zone. With this bigger target, our .30-06 will hit the top of our trajectory (8 inches high) at 190 yards if we zero at 350 yards. MPBR then extends to 412 yards. Our .300 RUM will peak 8 inches high at 220 yards, fall 8 inches low at 475 yards—its MPBR a long, 63-yard advantage for the magnum.
Using a 6-inch vital zone for a coyote, we’d have to scale back the .30-06 to a 235-yard zero. That would put the bullet 3 inches high at 145 yards and 3 inches low at 275 yards. If we zero the .300 RUM at 272 yards, we hit the top of trajectory at 170 yards and don’t strike 3 inches low until 320 yards—a 45-yard MPBR advantage over the .30-06.
This, then, is the biggest reason to shoot a magnum or any high-velocity cartridge using the sleekest, highest B.C. bullets that deliver the terminal performance you need. The combination extends MPBR, making it easy to aim dead center and shoot quickly with a high probability of scoring unless your target is a ridiculous distance away. Given that most of us can easily get within 400 or even 300 yards of the animals we’re pursuing, MPBR and a magnum can cover nearly all of our shooting needs.
An average mule deer’s chest is 17 inches deep, so a 10-inch target zone for MPBR
leaves room for miscalculations or imprecise shooting.
As with any sighting system, you must learn and practice MPBR before becoming proficient afield. And when setting up your target diameter, be conservative. Take into consideration your rifle’s inherent bullet distribution capabilities, plus your ability to shoot precisely from field positions. Both can add an MOA or 2 to the size of your safe target zone.
One of my favorite tactics is to combine MPBR with ballistic reticles or turrets. By choosing a conservative target diameter like 6-inches and zeroing a rifle for that, I usually push MPBR to 300 yards or slightly more. That lets me save ballistic reticles for ranges well beyond, starting at about 350 yards. Zeroing a ballistic reticle at 100 yards just wastes the first two sub reticles.