What is the MPBR...
The definition of Maximum Point Blank Range (MPBR) - the word "Maximum" is indeed the heart of the concept - is to indicate the longest distance one can shoot with the trajectory not going higher or lower than a defined "vital area".
This is why, I speak of MPBR for a 6" vital area in the context of small PG.
This, by definition, implies a point of impact no higher than 3" and no lower than 3" above or below the point of aim, and is appropriate for small game with ~6" vital areas.
Medium size game can be hunted with a MPBR for a 8" vital area, and large game can be hunted with a MPBR for a 10" or even, conceptually, a 12" vital area.
Evidently, a MPBR for a 8" vital area is longer than a MPBR for a 6" vital area; a MPBR for a 10" vital area is longer than a MPBR for a 8" vital area; etc. but their highest and lowest path above or below point of aim are also 4" and 5" instead of 3".
Contrarily to what many hunters believe, many game animals have a vital area (much) larger than 6" or even 8" or 10". For example, Jack O'Connor's, in his book
The Hunting Rifle, defines the vital areas of common game as
--- Pronghorn / small deer / small African antelopes: ~8" to 9"
--- Medium size deer / medium African antelope: ~10" to 11"
--- Large deer / North American wild sheep / mountain goat: ~11" to 14"
--- Elk / large African antelope: ~14" to 16"
--- Moose / Eland: ~18" to 21"
The MPBR was the best method up to the availability of
reliable consumer-grade (i.e. widely distributed and widely affordable):
1) chronographs;
2) laser range finders;
3) ballistic software;
4) turrets graduations on scope
The MPBR remains the best method if any of these 4 components is missing.
However, the MPBR is not without issues, the biggest one being that, often, hunters who use MPBR for large vital areas end up missing or crippling at shorter range (100 to 200 yards) by shooting too high.
--- A grand classic is that many forget in the heat of the moment that a MPBR aim applies to a heart shot located between 1/3 and 1/2 up the animal's thorax height. Any higher aim due to animal visibility of position necessitates compensating down for the MPBR high trajectory.
--- Another grand classic is hunters using a 8" or 10" MPBR because they are hunting medium size African antelope (say, Common Reedbuck, Blesbok, etc.), and missing high when they shoot along the way a small animal (say, Duiker, Mountain Reedbok, etc.).
--- Another even grander classic is people shooting over the animal when shooting the MPBR trajectory up or down steep slopes. It is classic in mountain hunting where shots can be taken at as much as 50 or 60 degree of angle to shoot well over the animal with a 8" MPBR when the hunter combines the mistakes in the heat of the moment of 1) forgetting to compensate for the MPBR high trajectory on small animals that only show the top half of their body; and 2) forgetting that a 60 degree, up or down, 300 yard shot is the equivalent to only a 150 yard shot, where the MPBR trajectory will often be close to reaching its highest point.
I am sure many people get everything always right in all circumstances, but, believe you me, I have unintentionally spined enough game I was taking a double lungs/heart shot at, to be fully aware of the intricacies of the MPBR even though I kept using it for 40 years, as the best method until first reliable/affordable laser range finders, then reliable/affordable chronographs, then reliable/affordable ballistic software (think iPhone or equivalent, and tablets) and finally reliable turrets graduations on affordable scopes came long, the last one being - counterintuitively I might add - only very recent (a few years at most) on civilian scopes.
Praise be to the MPBR - yes, "Maximum" defines its concept - but admittedly technology has finally made it obsolete, although like pre-WWI British classic doubles, I expect it to be still used for another century
There is peace of mind with a laser range finder that calculates the "ballistic distance" based on visual distance + barometric pressure (i.e. altitude) + angle of the shot + temperature (although temperature, unless truly extreme, is less important); simply turning the turret to that distance; and simply putting the crosshair where the shot needs to go
As I said earlier, I am not changing the older scopes (from 1980 Zeiss 1.5-6x42 to various S&B or Swarovski 1990's, 2000's, 2010's, and, for example, I still am very comfortable hunting Moose with a .340 Wby equipped with a scope sighted for a 8" MPBR (+ or - 4" trajectory over or below point of aim from 0 to 340 yards with 225 gf TTSX) because I have no tag to shoot anything else during a Moose hunt. I guess I could us a 10" or even 12" MPBR, but I dare not hutting with of POI (point of impact) + or - 6" from POA (point of aim)...
However, my .375 H&H, .300 Wby and .257 Wby Blaser R8 barrels all have a BDC (bullet drop compensation) turret, and yes, truly, it is simpler, and more reliable, than the MPBR because it takes the trajectory drop out of the hunting equation
