Point-blank range
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- For other uses see Point Blank (disambiguation)
In external ballistics, point-blank range is the distance between a firearm and a target of a given size such that the bullet in flight is expected to strike the target without adjusting the elevation of the firearm (see also gun). The point-blank range will vary with the firearm and its particular ballistic characteristics, as well as the target chosen. A firearm with a flatter trajectory will permit a nearer minimum and further maximum point blank range for a given target size, while a larger target will allow for a longer point blank range for a given firearm.
In forensics and popular usage, point-blank range has come to mean extreme close range (i.e., target within about a meter (3 feet) of the muzzle at moment of discharge but not close enough to be an actual contact shot). Gunshot wounds from point-blank are identified by extensive powder burns as well as tissue damage from perforation by unburned grains of gunpowder.
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[edit] History of term
The term originated from a precise, but slightly different, meaning in the 18th Century. The carriage of a cannon was normally constructed so that the muzzle was elevated slightly even when the carriage was on a horizontal surface and the elevation screw turned fully down. When it was fired, the ball would travel in a parabola, initially rising above the line of sight connecting the end of the barrel with the target. The point where it rose above the line — immediately in front of the muzzle — was called the first point blank primitive. The point where it fell below it, or sometimes where it struck the ground and bounced, was the second point blank primitive. Point blank range was the distance out to the second point blank primitive.
Point blank fire was fire at a target in which the gun did not need elevating. The target would lie either within point blank range, or slightly beyond it so that it would be hit by the first bound of the ball. It was felt that artillery was at its most effective against infantry or cavalry at this point as the unpredictably bouncing ball would be hard to avoid by a mass of troops. Different types of guns had different point blank ranges; for example point blank range was out to 342 yards (313 m) for a French 8 pound Gribeauval gun with a 2.25 pound (1.0 kg) gunpowder charge.
Fire at targets beyond point blank range was called direct fire, and would require the gun to be elevated.
In naval engagements, point-blank range was almost exclusively used from genesis of naval guns until the development of an effective self-propelled torpedo in the 1870s, even though the guns were actually capable of much greater ranges. Because a torpedo hit from a small vessel could sink even a large ship, the gun ranges anticipated for naval warfare opened out so that a ship would not be vulnerable to torpedo attack from its opponent. The range settled at around 6000 yards (5500 m) at the end of the 19th Century but during the First World War jumped to the limit of the range of the guns themselves, 15 miles (24 km) or more for larger calibres.
The need to measure and allow for the target's movement relative to the vessel carrying the gun led to much technical development in the period between about 1910 and the end of the Second World War. The most important one of these was the use of a separate organisation for aiming the guns, rather than the gunners themselves doing this using sights connected to the gun barrels. At the greater ranges the targets were no longer even visible to the gunners, crew in director towers or using radar now observing and correcting for the fall of shot. This in turn led on to further developments to perform the task in anti-aircraft fire where the ranges were nearly as great but the targets moved even more quickly.
[edit] Small arms and maximum point blank range
Small arms are often sighted-in so that the sight line and bullet path are within a certain acceptable margin out to the longest possible range, called the maximum point blank range. The range of distance inside the maximum point blank range is greatly dependent on the external ballistics of the cartridge in question; high velocity rounds have long point blank ranges, while slow rounds have much shorter point blank ranges. Other factors in the point blank range are the target size (which determines how far above and below the light of sight the trajectory may deviate), the height of the sights, and an acceptable drop before a shot is ineffective.
[edit] Maximum point blank range for hunting
A large target, like the vitals area of a deer, allows a deviation of a few inches (as much as 10 cm) while still ensuring a quickly disabling hit. A varmint such as a prairie dog requires a much smaller deviation, less than an inch (about 2 cm). The height of the sights has two impacts on point blank range. If the sights are lower than the allowable deviation, then point blank range starts at the muzzle, and any difference between the sight height and the allowable deviation is lost distance that could have been in point blank range. Higher sights, up to the maximum allowable deviation, push the maximum point blank range further from the gun. Sights that are higher than the maximum allowable deviation push the start of the point blank range out from the gun; this is quite common on varmint rifles, where close shots are never made, as it places the point blank range out to the expected range of the targets.
[edit] Maximum point blank range for military use
This sight setting for maximum point blank range is also referred to in the military as Battle Zero. Soldiers are instructed to fire at any target within this range by simply placing the sights on the center of mass of the enemy target. Any errors in range estimation are tactically irrelevant as a well-aimed shot will hit the torso of the enemy soldier. The current trend for elevated sights and higher velocity cartridges in assault rifles is in part due to a desire to extend the maximum point blank range, which makes the rifle easier to use.
[edit] Calculating point-blank range
A projectile falls due to gravity once it leaves a weapon barrel. All objects at the same geographic location fall with the same acceleration, denoted g, roughly 9.8 m/s2 (32 ft/s2). Velocity is a vector; the vertical component of any projectile's velocity can be treated separately from the horizontal component. If the barrel is horizontal and at height h above the ground, then Newton's Equations of Motion can be used to show that the range is approximately 
, where v is the muzzle velocity. This calculated range is reduced by air resistance, which depends on the shape of the projectile.
[edit] References
- Nosworthy, Brent. Battle tactics of Napoleon and his enemies. Constable and Co. Ltd, 1995 ISBN 0-09-477240-1
