Hollow-point bullet

A hollow-point bullet is a type of expanding bullet used for controlled penetration, where over-penetration could cause collateral damage (such as aboard an aircraft). In target shooting, they are used for greater accuracy due to the larger meplat. Hollow point bullets are more accurate and predictable compared to pointed bullets which, despite having a higher ballistic coefficient (BC), are more sensitive to bullet harmonic characteristics and wind deflection.
Plastic-tipped bullets are a type of (rifle) bullet meant to confer the aerodynamic advantage of the spitzer bullet (for example, see very-low-drag bullet) and the stopping power of hollow point bullets.
Mechanism of action.
Expansion.
When a hollow-point hunting bullet strikes a soft target, the pressure created in the pit forces the material (usually lead) around the inside edge to expand outwards, increasing the axial diameter of the projectile as it passes through. This process is commonly referred to as "mushrooming", because the resulting shape, a widened, rounded nose on top of a cylindrical base, typically resembles a mushroom.
The greater frontal surface area of the expanded bullet limits its depth of penetration into the target, and causes more extensive tissue damage along the wound path. Many hollow-point bullets, especially those intended for use at high velocity in centerfire rifles, are "jacketed", i.e. a portion of the lead-cored bullet is wrapped in a thin layer of harder metal, such as copper, brass, or mild steel. This jacket provides additional strength to the bullet, increases penetration, and can help prevent it from leaving deposits of lead inside the bore. In "controlled expansion" bullets, the jacket and other internal design characteristics help to prevent the bullet from breaking apart; a fragmented bullet will not penetrate as far.
Accuracy.
For bullets designed for target shooting, some such as the Sierra "Matchking" incorporate a cavity in the nose, called the meplat. This allows the manufacturer to maintain a greater consistency in tip shape and thus aerodynamic properties among bullets of the same design, at the expense of a slightly decreased ballistic coefficient and higher drag. The result is a slightly decreased overall accuracy between bullet trajectory and barrel direction, as well as an increased susceptibility to wind drift, but closer grouping of subsequent shots due to bullet consistency, often increasing the shooter's perceived accuracy.
The manufacturing process of hollow-point bullets also produces a flat, uniformly-shaped base on the bullet which allegedly increases accuracy by providing a more consistent piston surface for the expanding gases of the cartridge.
Match or target hollow-point bullets are designed for precision "target" use and no consideration is given to their expansion or other terminal ballistic performance. The United States military uses open-tip ammunition in some sniper rifles due to its exceptional accuracy. This ammunition is arguably not prohibited by military convention in that the wounds that it produces are similar to full metal jacket ammunition in practice. 
Hollow-point boat-tail.
A hollow-point boat-tail bullet is a match-grade bullet design that uses the concept of a teardrop-shaped tail to give it a lower drag coefficient and make it produce less turbulence in its wake. Only the base of the bullet has a boat tail-like shape – the meplat is still pointed. Some hollow-point boat-tail bullets with longer, more aerodynamic profiles are known as very-low-drag bullets.
Testing.
Terminal ballistics testing of hollow point bullets is generally performed in ballistic gelatin, or some other medium intended to simulate tissue and cause a hollow point bullet to expand. Test results are generally given in terms of expanded diameter, penetration depth, and weight retention. Expanded diameter is an indication of the size of the wound cavity, penetration depth shows if vital organs could be reached by the bullet, and weight retention indicates how much of the bullet mass fragmented and separated from the main body of the bullet. How these factors are interpreted depends on the intended use of the bullet, and there are no universally agreed-upon ideal metrics.
History.
Solid lead bullets, when cast from a soft alloy, will often deform and provide some expansion if they hit the target at a high velocity. This, combined with the limited velocity and penetration attainable with muzzleloading firearms, meant there was little need for extra expansion.
The first hollow-point bullets were marketed in the late 19th century as "express bullets", and were hollowed out to reduce the bullet's mass and provide higher velocities. In addition to providing increased velocities, the hollow also turned out to provide significant expansion, especially when the bullets were cast in a soft lead alloy. Originally intended for rifles, the popular .32-20, .38-40, and .44-40 calibers could also be fired in revolvers.
With the advent of smokeless powder, velocities increased, and bullets got smaller, faster, and lighter. These new bullets (especially in rifles) needed to be jacketed to handle the conditions of firing. The new full metal jacket bullets tended to penetrate straight through a target causing less internal damage than a bullet that expands and stops in its target. This led to the development of the soft point bullet and later jacketed hollow-point bullets at the British arsenal in Dum Dum, near Calcutta around 1890. Designs included the .303" Mk III, IV & V and the .455" Mk III "Manstopper" cartridges. Although such bullet designs were quickly outlawed for use in warfare (in 1898, the Germans complained they breached the Laws of War), they steadily gained ground among hunters due to the ability to control the expansion of the new high velocity cartridges. In modern ammunition, the use of hollow points is primarily limited to handgun ammunition, which tends to operate at much lower velocities than rifle ammunition (on the order of versus over 2,000 feet per second). At rifle velocities, a hollow point is not needed for reliable expansion and most rifle ammunition makes use of tapered jacket designs to achieve the mushrooming effect. At the lower handgun velocities, hollow point designs are generally the only design which will expand reliably.
Modern hollowpoint bullet designs use many different methods to provide controlled expansion, including:
Legality.
The Hague Convention of 1899, Declaration III, prohibited the use in "international warfare" of bullets that easily expand or flatten in the body.
It is a common misapprehension that hollow-point ammunition is prohibited by the Geneva Conventions, as the prohibition significantly predates those conventions. The Saint Petersburg Declaration of 1868 banned exploding projectiles of less than 400 grams, along with weapons designed to aggravate injured soldiers or make their death inevitable.
Despite the widespread ban on military use, hollow-point bullets are one of the most common types of bullets used by civilians and police, which is due largely to the reduced risk of bystanders being hit by over-penetrating or ricocheted bullets, and the increased speed of incapacitation.
In many jurisdictions, even ones such as the United Kingdom, where expanding and any other kind of ammunition is only allowed to a Firearms certificate holder, it is illegal to hunt certain types of game with ammunition that does "not" expand.
United Kingdom.
Most ammunition types, including hollow-point bullets, are only allowed to a Section 1 Firearms Certificate holder. The Firearms Certificate Holder must have the calibre in question as a valid allowance on his or her licence. A valid FAC or Firearms Certificate allows the holder to use Ball, FMJ, Hollow Point and Ballistic tipped ammunition for range use and vermin control. A Firearms Certificate will only be issued to any individual who can provide good reason to the police for the possession of firearms and its ammunition. Until recently all expanding ammunition fell under Section 5 of the Firearms Act 1968 and was only allowed when conditions were entered onto an FAC holders licence by the police. This condition would allow expanding ammunition to be used for:
Some ammunition types are still prohibited under Section 5 of the Firearms Act 1968. Ammunition that explodes on impact or any ammunition that is intended for military use are examples of this.
Popular calibres used in the UK for vermin, fox and deer control are as follows:
.223 Remington, .243 Winchester, .308 Winchester, .22-250 amongst others, all using Hollow-point bullets. Many Rimfire calibres are also using expanding ammunition such as .22 Long Rifle, .22 Winchester Magnum Rimfire and .17 Hornady Magnum Rimfire.
United States.
The United States is one of few major powers that did not agree to IV-3 of the Hague Convention of 1899, and thus is able to use this kind of ammunition in warfare, but the United States ratified the second (1907) Hague Convention IV-23, which says "To employ arms, projectiles, or material calculated to cause unnecessary suffering", similar to IV-3 of the first Convention. For years the United States military respected this Convention and refrained from the use of expanding ammunition, and even made special FMJ .22LR ammunition for use in High Standard pistols that were issued to the OSS agents and the Savage Model 24 .22/.410 combination guns issued in the E series of air crew survival kits. After announcing consideration of using hollow point ammunition for side arms, with a possible start date of 2018, the United States Army began production of M1153 special purpose ammunition for the 9×19mm Parabellum with a jacketed hollow point bullet at per second for use in situations where limited over-penetration of targets is necessary to reduce collateral damage.
The state of New Jersey bans possession of hollow point bullets by civilians, except for ammunition possessed at one's own dwellings, premises, or other lands owned or possessed, or for, while and traveling to and from hunting with a hunting license if otherwise legal for the particular game. The law also requires all hollow point ammunition to be transported directly from the place of purchase to one's home or premises, or hunting area, or by members of a rifle or pistol club directly to a place of target practice, or directly to an authorized target range from the place of purchase or one's home or premises.
Winchester Black Talon controversy.
In early 1992, Winchester introduced the "Black Talon", a newly designed hollow-point handgun bullet which used a specially designed, reverse tapered jacket. The jacket was cut at the hollow to intentionally weaken it, and these cuts allowed the jacket to open into six petals upon impact. The thick jacket material kept the tips of the jacket from bending as easily as a normal thickness jacket. The slits that weakened the jacket left triangular shapes in the tip of the jacket, and these triangular sections of jacket would end up pointing out after expansion, leading to the "Talon" name. The bullets were coated with a black colored, paint-like lubricant called "Lubalox," and loaded into nickel-plated brass cases, which made them visually stand out from other ammunition. While performance of the Black Talon rounds was not significantly better than any other comparable high performance hollow-point ammunition, the reverse taper jacket did provide reliable expansion under a wide range of conditions, and many police departments adopted the round.
Winchester's "Black Talon" product name was eventually used against them. After the high-profile 1993 101 California Street shooting in San Francisco, media response against Winchester was swift. "This bullet kills you better", says one report; "its six razorlike claws unfold on impact, expanding to nearly three times the bullet's diameter".
A concern was raised by the president of the American College of Emergency Physicians (ACEP) that the sharp edges of the jacket could cut medical personnels’ skin and risk spread of disease. An ACEP spokesman later said he was not aware of any such cases.
Winchester responded to the media criticism of the Black Talon line by removing it from the commercial market and only selling it to law enforcement distributors. Winchester has since discontinued the sale of the Black Talon entirely, although Winchester does manufacture very similar ammunition, the Ranger T-Series and the Supreme Elite Bonded PDX1.
Terminology.
The hollow point and soft-nosed bullets are both sometimes also referred to as dum-dums, so named after the British arsenal at Dum Dum, in present north Kolkata, India, where it is said jacketed, expanding bullets were first developed. This term is rare in North America, but can still be found in use, usually in the news media and sensational popular fiction, as well as in video games (such as Crimson Skies).
Many shooters refer to hollow points as "JHPs", from the common manufacturer's abbreviation for "jacketed hollow point".