A normal 9mm firearm will typically have a maximum chamber pressure of 35,000 pounds per square inch (psi). By using stronger, more powerful gunpowders +P ammunition increase chamber pressure for a 9mm firearm to up to 38,500 psi—a 10 percent increase. This increases the bullet’s velocity and the ability to incapacitate the target. The downside is that not all firearms are engineered to withstand repeated use of very high pressure ammunition, and +P ammunition can lead to increased wear and tear.

(The following is a series of three post combined that were published over the last few months.) 

The Best Military Rifles

Warfare in the post-9/11 period is primarily infantry-focused, with ground troops taking part in small-unit actions against insurgents and guerrillas. Fought on a wide variety of terrain, from arid desert regions to jungles and even cities, infantrymen have relied on their service rifles to get the mission done. Here are five of the best weapons, and how the wars of the twenty-first century changed them.

M4 Carbine:

Originally developed by Colt to fulfill a contract for the UAE, the M4 carbine was later accepted into U.S. Army and Marine Corps service. The M4 carbine is very similar to the M16A2 assault rifle, but features a shorter 14.5-inch barrel as opposed to the twenty-inch barrel of the M16. Like the M16A2, the M4 carbine fires the 5.56-millimeter round from a thirty-round magazine and has both semiautomatic and three-round-burst modes. Recently, as a result of battlefield experience with the M4, the U.S. Army decided to upgrade the weapons to the M4A1 standard. The -A1 carbines have thicker barrels for accuracy retention during sustained fire, an improved trigger, ambidextrous safety controls and the ability to fire on full automatic.

SA80A2 Rifle:

The primary service weapon of the UK’s Army, Navy and Air Force, the SA80 assault rifle was first fielded in the 1980s as a replacement for the L1A1 battle rifle. The rifle is a bullpup-configuration weapon, with the magazine and action positioned behind the trigger group. This allows for a more compact weapon system. Like the M4A1, the SA80A2 fires the 5.56-millimeter round and can accept the same magazine. Unlike the American carbine, the British one uses a short-stroke gas-piston system. In 2002, the weapons were upgraded to address a variety of shortcomings, including a modified bolt, extractor and hammer assembly, vastly increasing weapon reliability. In addition to the UK forces the SA80 has been sold to a number of Commonwealth countries, but overseas sales largely never materialized.

FAMAS:

The Fusil d’Assaut de la Manufacture d’Armes de Saint-Étienne, or FAMAS assault rifle, was adopted by France in the late 1970s. The assault rifle was a bullpup configuration, like the SA80A2, that came standard with twenty-five-round 5.56-millimeter magazines. Manufactured by GIAT, the rifle had an overall length of twenty-nine inches with a nineteen-inch barrel—nearly rifle length. The weapon weighed only 7.96 pounds. Intriguingly, unlike standard infantry assault rifles, FAMAS has radioactive tritium sights for night firing and a built-in bipod with arms that swivel up and store above the barrel. FAMAS’s blowback action gives it greater recoil than other weapons in this category. FAMAS is currently being replaced in French Army service by the Heckler and Koch 416.

HK416/M27

The Heckler and Koch 416 assault rifle is arguably a step up from the M4 carbine. Outwardly similar to the M4 in appearance, internally the rifle uses a gas-piston operating system, not the direct-impingement system used by the M4. This allows the rifle to run cooler and require less cleaning of the upper receiver, although it does reportedly make the 416 slightly front heavy. While the M4 and HK416 both share the same ammunition magazines and 5.56-millimeter round, the 416 has a longer sixteen-inch barrel, imparting a slight increase in range and velocity to the German-made weapon. The 416 is designated the M27 Infantry Automatic Rifle in U.S. Marine Corps service, and is being issued to all Marine infantrymen.

Recommended: The Colt Python: The Best Revolver Ever Made?

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Recommended: Smith & Wesson's .44 Magnum Revolver: Why You Should Fear the 'Dirty Harry' Gun

AK-47M:

The standard weapon of the Russian Ground Forces is the AK-74M. Developed in the 1970s as a replacement for the iconic AK-47, the main difference between the two weapons was the use of smaller, lighter 5.45-millimeter ammunition. The weapon, equipped with a thirty-round magazine, saw extensive use in the Soviet occupation of Afghanistan and was issued to frontline Soviet Units, particularly airborne, naval infantry and Germany-based conventional army units. The rifle has a side folding stock, 16.3-inch barrel and an overall length of thirty-seven inches. In 2015, the Russian Army adopted a number of Western-style upgrades to the AK-74M, including a skeletonized stock with adjustable cheek weld, a rail accessory mounting system similar to that on the M4 developed by Piccatinny Arsenal, foregrip and improved muzzle brake.

The revolver was one of the first multi-shot handguns. The revolver concept was preceded by the so-called “pepperbox” handgun, which used multiple barrels to arm an individual with multiple ready-to-fire bullets. This was later refined to the revolver concept, which saved weight by using a single barrel served by a revolving, cylindrical magazine holding six or more bullets. Although semiautomatic pistols have overtaken revolvers on the U.S. market, there are several good revolver designs that command attention. Simpler, less prone to jamming and capable of firing more powerful ammunition than the semiautomatic, revolvers still have their place.

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The 5 Best Revolvers

Ruger LCR

The Ruger LCR was introduced in the mid-2000s as a lightweight, concealable self-defense weapon. Just 13.5 ounces and 6.5 inches long, the LCR fits easily into a pocket, hip or ankle holster. Like most small revolvers, it has a five-round cylinder. Ruger originally introduced the LCR in .38 +P configuration, meaning it can fire both typical .38 Special ammunition and higher-pressure, harder-hitting +P rounds. The gun’s 1.87-inch barrel, aluminum and polymer frame, and corresponding light weight make it the easiest of the pocket revolvers to shoot, although it still has a considerable amount of recoil. The double-action design means a single pull of the trigger will advance the cylinder to a fresh round and cock the pistol. As a result the LCR lacks a hammer, making it easier to draw from behind clothing without snagging.

Smith & Wesson 686

One of the most popular revolvers in production, the Smith & Wesson 686 revolver is a medium (“L frame”) revolver chambered in the powerful .357 Magnum caliber. The 686 is designed to handle the heavier magnum round while pairing it with a heavier barrel and a six-round cylinder. Like all .357 Magnums, the 686 can shoot the less powerful .38 Special ammunition. The 686 features a four-inch barrel, has an overall length of 9.6 inches and weighs two-and-a-half pounds. It also adjustable sights, a double-action firing system and a stainless steel finish. A deluxe model comes with a larger, seven-round cylinder.

Ruger GP100

Sturm Ruger’s answer to the Smith & Wesson 686, the Ruger GP100 was introduced in the early 1990s. The GP100 was the successor to Ruger’s Security Six and Speed Six pistols, but uses a large frame very similar to the 686’s L frame. The GP100 is slightly heavier and the design slightly more angular than the 686, but it makes an excellent introduction to full-size revolvers and an outstanding home-defense weapon. The GP100 has since branched out into many other calibers, including .22LR, .327 Federal Magnum .and 44 Special.

Ruger Blackhawk

Sturm Ruger’s other line of popular revolvers has a distinctly Old West flavor to it. The Ruger Blackhawk line of pistols look similar to the old Western Colt Single Action Army revolvers of the nineteenth century, but with a host of modern features to keep them viable in the twenty-first. Cold hammer-forged barrels and a stout, beefy frame make the Blackhawk a manageable firearm in .357 Magnum, .41 Remington Magnum, the traditional cowboy calibers .45 Colt and, unusually, the World War II–era .30 Carbine. Like old-time cowboy revolvers, the Blackhawk’s cylinder must be loaded through a loading gate.

Taurus Model 85 Ultra-Lite

Although the semiautomatic pistol market has a large number of foreign competitors, Taurus is the only major overseas player in the revolver market. Among the Brazilian company’s many offerings, the most popular is the Model 85 Ultra-Lite. The Model 85 is a good choice as a home-defense handgun or concealed-carry piece, in the same class as the Ruger LCR. The .38 Special pistol can handle +P ammunition, with a five-round cylinder and comfortable rubber grips. The Model 85 is seven ounces heavier than the LCR but, unlike Ruger’s compact revolver, has a hammer allowing for single-action operation. This allows the Model 85 to be cocked first with a hammer, resulting in a much lighter trigger pull.

Since their invention in the tenth century, engineers, soldiers and tinkerers have constantly tried to make firearms more deadly. Typically that involves moving to heavier bullets driven by more powerful gunpowders, and while that is effective it is also louder, generates more recoil and necessitates new firearms. One solution is the creation of newer, deadlier ammunition for existing guns.

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5 Most Deadly Bullets

Dum Dum Bullets

Dum Dum bullets were developed for use by British and colonial forces on India’s Northwest Frontier in the 1890s. The infamous bullet design was created by the Dum Dum Arsenal, located just outside Calcutta. Dum dums consist of an ordinary copper jacketed lead bullet with the lead exposed at the nose, usually through a deep x-shaped cut in the nose. The theory is that upon impact, the lead slug expands and mushrooms to a much wider diameter than the bullet itself. The mushrooming also generates sharp points that cause grievous wounds passing through human flesh.

The 1899 Hague Declaration concerning Expanding Bullets was an attempt to ban dum dum–type bullets for use in military conflicts on the grounds they caused especially severe wounds. The declaration language targets “bullets with a hard envelope which does not entirely cover the core or is pierced with incisions.” One informal test determined that dum dums were “probably” more lethal but not as lethal as modern jacketed hollow points. Dum dum bullets were reportedly used by the People’s Liberation Army’s 27th Army against civilians during the 1989 Tiananmen Square massacre.

Jacketed Hollow Point Bullets

An evolution of the dum dum bullet, jacketed hollow points are copper-jacketed bullets with a hollow opening at the tip revealing the lead core. Upon contact with the target, the tip of the bullet blossoms into hydra-shaped object much larger than the original bullet, creating much larger wounds than nonhollow point bullets. In addition to expansion, some hollow points are also designed to fragment, causing multiple wound channels and even greater physical harm.

Jacketed hollow points are considerably more lethal than regular bullet ammunition. While hollow points have never caught on with regular military forces they are quite common in the self-defense market. Some hollow point rounds—such as Hornady Critical Defense ammunition—have a polymer dot in the center of the opening to aggressively drive bullet expansion.

13mm Gyrojet

During the late 1960s a small group of weapons engineers developed the 13mm gyrojet round, a large rocket powered bullet. A very large round over half-an-inch wide and an inch-and-a-quarter long, the Gyrojet round had a primer that ignited four canted rocket boosters, sending the entire projectile downrange at the target. The round weighed 25 percent more than a 7.62x51 rifle round and had a top speed of 1,250 feet per second.

Unlike traditional firearm cartridges, which leave the muzzle at maximum speed and gradually lose velocity, the Gyrojet rocket left the muzzle at a very slow speed and took approximately fifteen feet to reach maximum velocity. The Gyrojet pistol was reported tested by the U.S. Army’s Military Assistance Command Vietnam—Studies and Observation Group (MACV-SOG) but was not widely adopted.

Flechette Rounds

During the Vietnam War the U.S. Military issued 90 and 105mm antipersonnel rounds packed with tiny darts to tank and tank destroyer crews. Upon firing, the so-called “flechette” rounds would send a high speed cloud of deadly darts downrange. Flechette rounds were particularly useful against human wave attacks, although they do cause higher than normal wear and tear on barrels.

The Special Purpose Individual Weapon (SPIW) program of the mid-1960s saw the flechette round brought down to the individual soldier level with the testing of the M19 experimental rifle and the XM645 flechette round. The XM645 was a .070 inch steel needle bedded in a fiberglass sabot, much like a modern kinetic energy anti-tank round. The flechette was fin-stabilized, making it highly accurate. It also tended to bend into a u-shape when striking human flesh, causing large and often lethal wounds. The program was shelved due to the difficulty in making the flechette at an affordable cost.

+P ammo

Unlike specialized ammunition types, +P ammunition is simply regular ammunition made more deadly by increasing chamber pressure. Normally, bullets are sent flying out of the barrel of a gun by the burning of gunpowder. The gunpowder burn rapidly builds up pressure inside the firearm, sending the bullet out of the barrel at hundreds if not thousands of feet per second.

A normal 9mm firearm will typically have a maximum chamber pressure of 35,000 pounds per square inch (psi). By using stronger, more powerful gunpowders +P ammunition increase chamber pressure for a 9mm firearm to up to 38,500 psi—a 10 percent increase. This increases the bullet’s velocity and the ability to incapacitate the target. The downside is that not all firearms are engineered to withstand repeated use of very high pressure ammunition, and +P ammunition can lead to increased wear and tear.

Kyle Mizokami is a writer based in San Francisco who has appeared in The Diplomat, Foreign Policy, War is Boring and The Daily Beast. In 2009 he cofounded the defense and security blog Japan Security Watch. You can follow him on Twitter: @KyleMizokami.