Projectile Tech 101: A two-part series / Sgt. James Spitzer (Retired)

In the world of Forensic Science, part of the job of a Firearms Examiner is to wade through a sea of myths and misconceptions to deliver the genuine facts into the hands of an often bewildered jury. This is never more problematic than when dealing with bullets. They represent some of our greatest creative engineering achievements, and also some of our lowest destructive impulses.  Bullet folklore is never in short supply, but the unvarnished truth can be illusive.  What follows are a few of the basics, without the spin.

Photo credit: Alvimann from morguefile.com

Photo credit: Alvimann from morguefile.com

A bullet is a hard projectile which is propelled through the barrel of a firearm by rapidly expanding gasses created by burning gunpowder (this is known as interior ballistics).  After it exits the barrel, it seeks out some generic destination known only as ‘downrange’ (this is known as exterior ballistics).  What it does when it gets there (this is known as terminal ballistics) is a function of how that projectile is constructed.  There are a multitude of subtle variations in design, each devised to perform a specific task inside the barrel, in the air, or at impact.

A gun barrel is simply a steel tube with a series of helical grooves inside of it, known as rifling. The purpose of these grooves (and the area between them, known as lands) is to bite into the sides of the bullet and to force it to follow their spiral path down the barrel.  As it exits the barrel spinning (at up to 30,000 RPM), it flies the way that Peyton Manning throws a football, rather than tumbling end over end. This gyroscopic stability is what gives a bullet accuracy and precision.

The first and simplest category of projectile is the Non-Expanding variety of bullet, and the most basic of these is the solid Lead Bullet.  Lead is a common component because it is cheap, plentiful, and heavy enough to transfer a significant amount of kinetic energy to its target.  At handgun velocities, it is ideal in that it is soft enough to conform to the unique contours of the inside of a gun barrel and form a gas seal as it engages the rifling.

The Round Nose Lead (RNL) Bullet is cylindrical with a rounded, conical nose for better aerodynamic properties.  The rear is often concave in order to form a better gas seal with the rifling when the pressure from the burning powder expands inside the base.

Bullet weights have historically been recorded in grains rather than some metric unit.  To give you a sense of what a grain is, a penny weighs 48 grains, and a traditional .38 Spl RNL Bullet weighs in at 158 grains.

The Wadcutter (WC) Bullet is also composed of lead, but is cylindrical with a flat nose, resembling a D-Cell battery in shape. The flat nose is intended to punch a nice, clean, cookie-cutter hole in a paper target, for easier scoring.

The Semi-Wadcutter (SWC) Bullet is a compromise between the two previous bullets with a conical front end that is truncated to a flat nose having a diameter smaller than that of the bullets’ base.  It is the middle ground between clean holes and clean aerodynamics.

Image courtesy of freedigitalphotos.net

A range of various bullets
Image courtesy of freedigitalphotos.net

The biggest limitation for lead as a bullet material is that it is relatively soft and has a low melting point, relegating it to lower velocity use, such as handgun cartridges. At speeds starting around 900 ft/s, common in handguns, the resulting friction causes bullet lead to smear and even become atomized to a vaporous form, which is deposited inside of the barrel, fouling the rifling. (Bullet velocities are commonly recorded in terms of Feet per Second (ft/s) rather than a metric measurement.  For the purpose of having a frame of reference, 900 ft/s = 614 mph.)  Alloying the lead with Antimony or Tin hardens the bullet, reducing this effect. However, with higher velocities, the greater the effect and the more fouling will be observed.

This gave rise to one variant of the lead bullet known as the Nyclad Bullet, which is a lead bullet with a thick, blue nylon coating on its surface to combat lead fouling.  They never caught on in a big way, but are still seen occasionally.

The real solution to lead fouling is the Jacketed Bullet.  These have a lead core for weight, but are overlaid with a thin layer of a harder metal such as Copper, Brass, Nickel, or even Steel.  You can picture it like an M&M where the lead core is analogous to the chocolate center, and the candy shell is the jacket.

The simplest form of Jacketed Bullet is the Full Metal Jacket (FMJ), also known as the Full Metal Case (FMC).  This is terminology is somewhat misleading because the metal jacket is not quite as full as it sounds. The lead core of the bullet is exposed at the base.

When the core is completely encapsulated in a metal jacket, it is known a Totally Metal Jacketed (TMJ) Bullet, which typically requires more complex manufacturing techniques, but TMJ Cartridges are not uncommon.

A variation of the Full Metal Jacket (FMJ) Bullet commonly seen in match grade rifle bullets is the Boat Tail (BT) Bullet.  This bullet typically has a traditionally pointed nose (known as a Spitzer nose), but the base end of the bullet is tapered down to a smaller diameter for better aerodynamic properties at high velocities.  This streamlining eliminates the drag caused by the vacuum created at the base of a conventional based bullet, and thus, enhanced range and accuracy.

One of the more exotic non-expanding rounds is the Tracer Bullet.  These have a hollow base filled with a flare-like substance, such as magnesium, which ignites when fired and burns briefly with a bright, vivid color in flight.  The purpose is to give the shooter a visual indication of the bullets’ path, typically in automatic fire.  Machine gun ammunition is often loaded so that every fourth cartridge is a tracer, making it easier to visualize the path of full-auto fire.

These are often confused with another non-expanding round known as an Incendiary Bullet which is not visible in flight, but has a flammable mixture in the nose which ignites on impact with a target.  These are designed to ignite any fuel, structures or munitions that they strike.  Obviously, these for are military use.

Armor Piercing (AP) Bullets are visually similar to other pointed Full Metal Jacket Bullets, but have a core made of a very hard, high density metal such as steel, tungsten, or depleted uranium.  They were designed to penetrate hardened steel armor plating and lightly armored vehicles, and are typically for Law Enforcement and Military applications. A common misconception is that they were banned for their ability to defeat body armor, and many were indeed banned from manufacture or import. They are, in fact, still legal in specific .223 and .30-06 rifle calibers. You cannot hunt with them, manufacture them, or import any more of them, but they are nevertheless legal to own and shoot.  If you find that confusing, you are not alone.  It may seem like common sense legislation to ban AP bullets, but the sad truth is that nearly any full metal jacket rifle bullet can readily penetrate soft body armor.

This brings us to the politically charged topic of Cop-Killer Bullets.  This unfortunate term is a nickname that has slipped into the vernacular mostly through repeated use by people trying to gin up civic outrage against the Firearm or Ammunition industry. Public perception seems to define it as a Teflon monster that could easily zip through half a dozen bulldozers, and would only stop after penetrating the heart of a Police Officer six weeks from retirement, or an innocent child.

The true facts begin in the mid 1960s with a handgun cartridge developed by police, for police use, to penetrate hard targets such as car windshields and doors.  The manufacturer, known as KTW, used a solid brass bullet to achieve this effect, but found that firing such a hard projectile produced excessive wear to the rifling.  To counteract this problem, they coated the bullet in Teflon, which protected the bore.

In the early 1980s it was determined that KTW bullets could defeat early forms of soft body armor. It turns out that this had little to do with the Teflon, as commonly believed, but rather the shape and velocity of the bullet.  After a high profile NBC exposé aired in 1982, banning the Cop-Killer bullet became a Cause Célèbre, culminating in a Federal Law specifically prohibiting KTW, THV and Arcane Handgun Cartridges. It should be noted, however, that in the history of KTW, from 1968 to 1986 when the Law was enacted, no Police Officer in body armor was ever killed with a KTW Bullet.

Another interesting variant of non-expanding bullet is the Sabot Cartridge, such as the Accelerator manufactured by Remington.  It is a .30 caliber cartridge, designed to fire a .223 caliber bullet out of a .30 caliber barrel at a higher velocity than normal, generating a flatter trajectory.  It accomplishes this magic trick by encasing the 55 grain bullet in a larger plastic enclosure (sabot) that drops off of the bullet a few inches after it exits the muzzle. The unique quality of the Accelerator is that the bullet itself never comes into contact with the rifling of the barrel, only the plastic sabot. The bullet that strikes the target is unmarked, and can’t be forensically linked to the rifle.  While Accelerator Cartridges are fairly uncommon, Sabot rounds are still quite common in muzzleloading applications.

I hope that this has dispelled a few misconceptions with regard to non-expanding bullets. The next segment will focus on Expanding Bullets.


Sgt. James Spitzer spent 37 years working as an Independent Consultant in the Forensic Discipline of Firearms Identification.  He now resides in Auckland, New Zealand and is best known for a high profile case that garnered national attention in 2003 in which he performed forensic examinations and subsequent courtroom testimony as Solicitor General’s Witness in a trial that led to the conviction of controversial Kiwi poacher Whitey “Chickenbone” Carter.


(The Killer Nashville Guest Blog series is coordinated by KN Executive Director Beth Terrell (http://www.elizabethterrell.com/).  To be a part of this series, contact Beth at beth@killernashville.com.)

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About Clay Stafford

Clay Stafford is an author / filmmaker (www.ClayStafford.com) and founder of Killer Nashville (www.KillerNashville.com). As a writer himself, he has over 1.5 million copies of his own books in print in over 14 languages. Stafford’s latest projects are the feature documentary “One of the Miracles” (www.OneOfTheMiracles.com) and the music CD “XO” (www.JefferyDeaverXOMusic.com). A champion of writers, Publishers Weekly has identified Stafford as playing “an essential role in defining which books become bestsellers” throughout “the nation’s book culture.” (PW 6/10/13)
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