Frangible Ammunition: A Composite Story
By Paul Evancoe
Surprisingly, recreational shooting is one of the safest hobbies in which one can participate. This is attributed to the shooting community’s common observance of basic firearms’ handling and range safety rules designed to prevent people from being accidently shot. However, even with the strict observance of firearms and range safety, there are other safety threats that can’t be completely eliminated, like exposure to airborne lead particulate and ricochets. Using frangible ammunition largely mitigates such problems, but in doing so it may, by design, possess some of its own.
Frangible rounds (bullets) are also known as Advanced Energy Transfer rounds (or AETs). The only difference between regular ammunition and frangible (AET) ammunition is the bullet. Frangible ammunition is produced in a wide variety of calibers and available (although it’s somewhat hard to find in stores) for both pistols and rifles. The only rifle rounds produced are in 5.56mm NATO and 7.62mm NATO, and its operational performance in actual combat is dubious.
There are only two frangible rounds that have been approved for U.S. military training purposes (not combat use) and they are 9mm and 5.56 NATO. That said, frangible pistol ammunition is produced in a wider range of calibers than its rifle counterpart calibers, because frangible rifle rounds, as a result of their high velocity, provide inconsistent performance. This includes issues like fragmenting early, bullet fracturing and subsequently jamming in the rifle, or other physical characteristics - more on this in a moment.
Frangible ammunition provides the best way to eliminate bullet over-penetration and thus, reduce liability for use by law enforcement and home protection. Frangible ammunition has been used in handguns and sub-machine guns by SWAT, hostage rescue teams and nuclear reactor and weapon storage facilities security forces, throughout the U.S. since its invention in 1974.
Both the law enforcement and civilian markets use frangible ammo for training, especially when shooting steel targets in close-quarter training. Copper jacketed lead bullets commonly ricochet off steel targets, presenting everyone close by with a potentially lethal safety hazard. In comparison, frangible bullets can be used at extremely close range (literally inches from the gun muzzle) on steel targets, with virtually no chance of ricochet.
Frangible, by definition means fragile or brittle, so how does that description work for bullets? Frangible bullets are designed to break up into small, less harmful, pieces upon contact with anything harder than they are. This maximizes the round's transfer of energy to the object and minimizes the chances that pieces of the bullet will exit the object at dangerous velocities. Each of the small fragments quickly loses any energy and therefore pose very little danger to any secondary targets. This means that full-power frangible bullets can be shot at muzzle-close distances without any worries that the bullet or bullet jacket will ricochet and cause injury to either the shooter or others within near proximity.
Most frangible bullets are formed by pressing a composite mix of hybrid materials together (powdered metals like bismuth, tin, copper, tungsten or steel, or lead shot,) with an adhesive binder under pressure, forming a "solid" bullet slug. That slug is often sheathed with a copper jacket that improves structural integrity by reinforcing the bullet walls. This copper jacket acts to hold the bullet together during factory cartridge loading, handling, gun loading, and when fired, the frangible bullet’s ballistic travel to its point of impact.
Non-lead bullets fabricated employing powder metallurgy simulants have proven to be one-to-one replacements for their lead analogs. Ammunition is commercially available that uses non-lead frangible bullets and propellant charges that match the performance of their traditional copper jacketed lead bullet counterparts. Velocity, chamber pressures and accuracy were found to be similar to those for the lead-body projectiles. The lesson here is that powder metallurgy provides greater flexibility in controlling bullets' properties. Processing conditions, composition, and powder particle size can be manipulated to alter bullet density, ballistic flight and impact behavior. The negative is that frangible bullets cost more to manufacture than traditional copper jacketed lead bullets.
In the 1990s, the Department of Energy's Oak Ridge National Laboratory (ORNL) developed a non-toxic, all-metal replacement for lead in bullets by using advanced powder metallurgy. ORNL used cutting edge forming technology borrowed from their nuclear weapons pit and explosives forming experience to produce metal-matrix composite simulants that have ballistic mass properties very similar to lead.
ORNL then developed a process to fabricate bullets from mixtures of powdered metals that are pressed at room temperature to produce a high-density consistent mass material. No heat treating or sintering is necessary to achieve densities and mechanical properties that mimic those of lead and its alloys. Mechanical interlocking and "cold welding" bond the metals together, and can be varied to control the properties of the lead replacement. Bullets can be pressed directly to finished tolerance bullet shape. These frangible bullets can be mass produced and further swaged to precision tolerance, with or without jacketing.
Another solution, perfected by and offered in the Glaser Safety Slug and other brands like the Mag Safe SWAT, is the use of a different style frangible bullet nose. Instead of a fully jacketed bullet with a metal nose, these bullets use a polymer nose, making them consistently more likely to fragment and dispel their contents when striking a person or hard surface.
While some frangible bullet designs are solid and will fragment as the composite in the bullet shatters, some like the Glaser Safety Slug, for example, are actually filled with #12 shot in the Blue line and #6 shot in the Silver line. This bullet design provides a more uniform impact and a more lethal wound cavity.
Another top manufacturer, Sinterfire, makes about 90% of the frangible bullets used in the U.S. Sinterfire’s Greenline frangible ammunition and is the “greenest” and cleanest across the entire frangible market. Their projectile contains no lead, so there’s no airborne lead particulate released when the bullet leaves the barrel. Sinterfire’s Greenline ammunition also uses a non-toxic primer that virtually eliminates any release of harmful toxic agents into the air resulting from the primer ignition process.
Sinterfire offers several styles of frangible bullets, ranging from fully jacketed semi-flat nose bullets to hollow point bullets. Their semi-flat nose bullets will only break up when they hit something as hard as themselves or harder. In contrast, their hollow point will begin to disintegrate when impacting objects like sheet rock and thin plywood paneling. Gel-block slow motion tests using this ammunition show the hollow point bullet nose coming apart upon gel-block surface impact to create multiple wound channels, while the bullet base impressively remains intact and penetrates deeper. In flesh, this means 100% of the round’s kinetic energy would be traumatically dumped into the point of impact.
The above said, what are some of the negatives associated with frangible ammunition? In addition to the obvious increased cost and on-the-shelf scarcity of frangible ammunition, the most important concern is its general overall lack of feed reliability when using frangible ammunition in semi-autoloading and or auto-loading firearms. Frangible’s unreliability results from the frangible bullet’s inherently weak structural integrity.
Weak bullet structural integrity can result in the bullet fracturing at the cartridge casing crimp line. If this happens it will almost always result in a feed malfunction, or if the cartridge happens to chamber with a fractured bullet, there will be two separate holes in the target resulting from the each half of the bullet. That means certain loss of accuracy and significantly reduced ballistic impact. Not all brands suffer from this physical characteristic, but many do.
Since frangible ammunition has different physical design characteristics that dictate its penetration and ballistic impact characteristics depending upon the manufacturer, be sure to check the different brands and read the small print to determine the type of frangible ammo that best meets your requirements. When you think you’ve narrowed it down, buy enough quantity (perhaps several hundred rounds) of it to shoot and evaluate operationally with the gun(s) you will be carrying. Insure it shoots reliably and doesn’t break off and jam your weapon. This is especially important for autoloading weapons and if you’re going to bet your life on frangible ammunition.
This article first appeared in Small Arms Review V21N5 (June 2017) |
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Walter.J.Kuleck |
Operation Pinball (Continued) |
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Walter.J.Kuleck |
Operation Pinball The first military use of frangible ammunition was during WWII in Operation Pinball. Two chemists at Duke University, Paul Gross and Marcus Hobbs, accepted the challenge of developing a frangible Cal..30 bullet with ballistic characteristics similar enough to Ball, M2 that it could be used in live fire training for bomber gunners. The result was the Cartridge, Caliber .30, Frangible, Ball, M22, with a bullet comprised of a Bakelite/lead matrix. The targets were |
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