Bullet Basics 1- Materials

Identifying the manufacturer and caliber of a submitted bullet is an important examination conducted in a forensic laboratory by Firearm and Toolmark Examiners.  We've discussed the term "caliber" on a previous page that can be found here.

There are a number of good reasons to determine who made the bullet but one that stands out to be of particular importance occurs when the bullet cannot be identified to a specific firearm through normal firearm identification techniques.  Let's say that several shots are fired at a crime scene and all of the shooters are firing GLOCK brand 9mm Luger caliber pistols.  In this situation all of the bullets collected will have the same diameter and will have the same general rifling characteristics. 

The only way in this situation to determine who may have fired one bullet vs. another is to look at the brand of ammunition that each shooter was using (hopefully they used different brands!) and then try to match the physical characteristics and materials to those used by one brand cartridge or the other. 

The fired cartridge cases collected at the scene have headstamps that will identify who made the cartridge case, so once they are identified to the gun they were fired from, we can look at the bullets to see if they are similar to bullets made by those manufacturers.

By identifying the bullet manufacturer we can now determine which gun most likely fired those bullets given the limited universe of this one crime scene.  Firearm examiners will examine the unknown bullets and compare the physical properties of the bullets to known standards.  Through this process of direct comparison often times the manufacturer can be determined and in doing so provide the investigation just one more clue to help bring the case to a desirable outcome.

There are several things that firearm examiners look for when they examine the bullets.  The diameter and weight are helpful in determining caliber, but the materials used and the general shape of the bullet can assist in determining the manufacturer of the unknown bullet.

Let's start with the materials used in the manufacture of bullets.

Bullet Materials

Projectiles in general have come along way over the last several centuries.  What started out as crude rocks and pebbles have steadily evolved into bullets born from very advanced engineering.  For some good information on the history of the bullet visit the Wikipedia.

It wasn't until the late 15th century that bullets were starting to be produced by casting metal into balls using molds.  The modern bullet can be manufactured through casting, swaging, milling, plating, stamping or compression processes. Bullets are usually made of a single metal alloy or a layered combination of various materials to include lead, copper, brass, bronze, steel, and aluminum.  These layered bullets are referred to as jacketed bullets.  The materials used in the manufacture of a bullet effect its performance both in flight and when they reach their target.

There are two very important things that manufacturers constantly try to strike a balance between.  They are penetration and expansion.  The type of target you are shooting at dictates the type of bullet you will use.  If a bullet fails to penetrate deep enough it may not reach the internal organs of the target and therefore not immobilize or kill the target.  Too much penetration and the bullet can pass through the target and continue down range wasting energy.

So manufacturers are constantly trying to design a bullet that does the best job for it's intended purpose.  The materials used in the manufacture of the bullet are very critical to achieving the goal of the bullets impact.

Non-jacketed Bullets- The most common material used in the manufacture of non-jacketed bullets is lead.  Lead bullets are usually an alloy of lead and antimony which is added to give the bullet some additional hardness.  Variations are the norm when it comes to the materials used in bullets and it's not uncommon to find lead bullets with a thin coating of copper or brass plating.  Bullets having this thin coating is sometimes referred to as a copper-washed or "Lubaloy" bullet.  This thin coating can be easily scratched away from the surface of the lead causing problems for firearm examiners when these bullets are damaged.  Another example of a coated bullet is the Federal "Nyclad" bullet that is designed to reduce lead emissions.

Plain Lead Round-nosed bullet	Copper-washed or "Lubaloy" lead round-nosed bullet		Federal "Nyclad" nylon coated bullet

Other solid bullets can be machined out of a piece of copper, brass, or similar material.  Newer manufacturing techniques use pressure to compress a material like tungsten into a bullet referred to as a "frangible" bullet. Examples of these can be seen below.

Jacketed bullets- Jacketed bullets are a laminate of material, with the harder "jacket" covering a core typically made of lead.  This jacket material differs from the thin copper plating seen on the copper-washed bullets above.  The jacket material cannot be easily removed.

The most common bullet jacket material is copper.  These can sometimes be plated with nickel to give the bullet a silver finish but the jacket can also be made of a number of other materials such as aluminum or steel.  Steel jackets are widely used in bullets that originate in the European and Chinese markets.  Steel jacketed bullets are usually coated or plated to help prevent rusting.

Jacketed bullets usually have an opening at the base or the nose but some are have no opening in the jacket material.  These bullets are called totally-metal-jacketed bullets (TMJ) or encapsulated bullets.

CCI totally-metal-jacketed bullet

The most common jacketed bullet core material is lead but exceptions again exist and a common example is the 7.62x39mm armor piercing bullet (show above right). This bullet has a steel jacket over a thin layer of lead which surrounds a steel core.  It is not uncommon for firearm examiners to receive just the steel core as an exhibit.  When this bullet strikes a target the steel core can punch right through the nose of the jacket material.  I had a case several years ago where several of these bullets were fired through the windshield of a car, killing the lone occupant.  All that was recovered from the victim were several steel bullet cores like those seen below.

Jacketed bullets may also contain something other than a lead or steel core.  Some may contain small lead pellets, plastic, or maybe even a silicone rubber material as seen below. 

Another somewhat unusual jacketed bullet is the Remington Accelerator.  This centerfire rifle bullet consists of a copper jacketed bullet that is of a smaller caliber than the rifle it is fired in.  This smaller bullet is surrounded by what is called a Sabot.  The sabot actually rides down the rifling of the barrel and once leaving the barrel of the rifle the sabot and the bullet separate.  The sabot falls to the ground fairly close to the rifle but the light weighted bullet travels down range at a high velocity minus any identifiable rifling characteristics.  They are on the sabot! 

Remington Accelerator "sabot" enclosed bullet

So as you can see the materials used in bullets can vary widely.  Just remember that the above examples are a mere drop in the bucket.  I have just briefly mentioned centerfire rifle bullets primarily because I don't receive many in casework.  Handgun centerfire and rimfire bullets are by far the most common projectiles seen in most forensic laboratories.

Now let's discus the shape of bullets.

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