of Smokeless Powders and their Forensic Analysis: A Brief Review
Bruce R. McCord
Associate Professor of Analytical and Forensic Chemistry
Department of Chemistry
are a class of propellants that were developed in the late 19th
century to replace black powder. The term smokeless refers to the
minimal residue left in the gun barrel following the use of smokeless
powder. In forensic analysis, smokeless powders are often encountered
as organic gunshot residue or as the explosive charge in improvised
powders can be placed into one of three different classes according
to the chemical composition of their primary energetic ingredients.
A single-base powder contains nitrocellulose, whereas a double-base
powder contains nitrocellulose and nitroglycerine. The energetic
ingredients in triple-base powders are nitrocellulose, nitroglycerine,
and nitroguanidine, but because triple-base powders are primarily
used in large caliber munitions, they are difficult to obtain on
the open market.
The major classes
of compounds in smokeless propellants include energetics, stabilizers,
plasticizers, flash suppressants, deterrents, opacifiers, and dyes
(Bender 1998; Radford Army Ammunition Plant 1987).
facilitate the explosion. The base charge is nitrocellulose, a
polymer that gives body to the powder and allows extrudability.
The addition of nitroglycerine softens the propellant, raises
the energy content, and reduces hygroscopicity. Adding nitroguanidine
reduces flame temperature, embrittles the mixture at high concentration,
and improves energy-flame temperature relationship.
prevent the nitrocellulose and nitroglycerine from decomposing
by neutralizing nitric and nitrous acids that are produced during
decomposition. If the acids are not neutralized, they can catalyze
further decomposition. Some of the more common stabilizers used
to extend the safe life of the energetics are diphenylamine, methyl
centralite, and ethyl centralite.
reduce the need for volatile solvents necessary to colloid nitrocellulose,
soften the propellant, and reduce hygroscopicity. Examples of
plasticizers include nitroglycerine, dibutyl phthalate, dinitrotoluene,
ethyl centralite, and triacetin.
- Flash suppressants
interrupt free-radical chain reaction in muzzle gases and work
against secondary flash. They are typically alkali or alkaline
earth salts that either are contained in the formulation of the
propellant or exist as separate granules.
coat the exterior of the propellant granules to reduce the initial
burning rate on the surface as well as to reduce initial flame
temperature and ignitability. The coating also broadens the pressure
peak and increases efficiency. Deterrents may be a penetrating
type such as Herkoteâ,
dibutyl phthalate, dinitrotoluene, ethyl centralite, methyl centralite,
or dioctyl phthalate; or an inhibitor type such as Vinsolâ
enhance reproducibility primarily in large grains and keep radiant
heat from penetrating the surface. They may also enhance the burning
rate. The most common opacifier is carbon black.
- Dyes are
added mainly for identification purposes.
composition is one important
- Other ingredients
may be one of the following:
- A graphite
glaze used to coat the powder to improve flow and packing
density as well as to reduce static sensitivity and increase
erosion coatings applied as a glaze to reduce heat transfer
to the barrel, but uncommon in small-arms propellants
aid coatings that are most commonly used in ball powders to
improve surface oxygen balance
characteristic defining smokeless propellants; however, another important
characteristic is its morphology. Shape and size have a profound effect
on the burning rate and power generation of a
powder (Meyer 1987). Common particle shapes of smokeless propellants
include balls, discs, perforated discs, tubes, perforated tubes, and
aggregates (Bureau of Alcohol, Tobacco and Firearms 1994; Selavka
et al. 1989). A few common types of smokeless powder morphologies
can be seen in Figure 1 (Bender 1998).
lends clues to whether a powder is single- or double-base (Bender
1998). Most tube and cylindrical powders are single-base, with the
exception of the Hercules Reloaderâseries.
Disc powders, ball powders, and aggregates are double-base, with
the exceptions being the PB and SR series powders manufactured by
IMR Powder Company of Plattsburg, New York.
Except for ball
powder, smokeless powder is manufactured by one of two general methods,
differing in whether organic solvents are used in the process (Meyer
1987; Radford Army Ammunition Plant 1987). A single-base powder
typically incorporates the use of organic solvents. Nitrocellulose
of high- and low-nitrogen content are combined with volatile organic
solvents, desired additives are blended with them, and the resulting
mixture is shaped by extrusion and cut into specified lengths. The
granules are screened to ensure consistency, and the solvents are
removed. Various coatings, such as deterrents and graphite, are
applied to the surface of the granules. The powder is dried and
screened again, then blended to achieve homogeneity.
of double-base powders requires the addition of nitroglycerine to
the nitrocellulose. Two methods can be used. One method uses organic
solvents, the other uses water. The organic solvent method mixes
nitrocellulose and nitroglycerine with solvents and any desired
additives to form a doughy mixture (Meyer 1987; National Research
Council 1998; Radford Army Ammunition Plant 1987). The mixture is
then pressed into blocks that can be fed into the extrusion press
and cutting machine. The resulting granules are screened prior to
solvent removal and the application of various coatings. The powder
is dried, screened again, then blended to achieve homogeneity. The
water method adds the nitroglycerine to a nitrocellulose water suspension
to form a paste (Meyer 1987; Radford Army Ammunition Plant 1987).
The water is removed by evaporation on hot rollers, then the dried
powder is shaped by extrusion and cutting.
powders use a solvent-based process similar to the double-base powder
process (Meyer 1987; Radford Army Ammunition Plant 1987). Nitrocellulose
and nitroglycerine are premixed with additives prior to the addition
of a nitroguanidine solvent mixture. The nitroguanidine is incorporated
into the overall mass without dissolving in the other materials.
The final mixture is then extruded, cut, and dried.
of smokeless ball powder requires a more specialized procedure (National
Research Council 1998). Nitrocellulose, stabilizers, and solvents
are blended into a dough, then extruded through a pelletizing plate
and formed into spheres. The solvent is removed from the granules,
and nitroglycerine is impregnated into the granules. The spheres
are then coated with deterrents and flattened with rollers. Finally,
an additional coating with graphite and flash suppressants is applied,
and the batch is mixed to ensure homogeneity.
In the manufacturing
process, smokeless powders are recycled and reworked (National Research
Council 1998). When a powder within a batch is found to be unsatisfactory,
it is removed and returned to the process for use in another lot.
Manufacturers save money by recycling returns by distributors or
the return of surplus or obsolete military powders. Hence, reworking
and recycling the material assures good quality control of the final
product, reduces costs by reusing materials, and reduces pollution
by avoiding destruction by burning.
of smokeless powders is big business in the United States, where
approximately 10 million pounds of commercial smokeless powders
are produced each year. Most of the powder is sold to the original-equipment
manufacturers to be used for manufacturing ammunition. A large amount
is sold to domestic and foreign militaries (National Research Council
1998). The rest is sold in individual canisters (ranging from ½-pound
cans to 12- or 20-pound kegs) to gun stores or hunting and shooting
clubs for hunters and target shooters who prefer to hand load their
There are several
ways smokeless powders are distributed within the United States
(National Research Council 1998). Some manufacturers, foreign or
domestic, produce, package, and sell their own powders commercially.
They may also sell in bulk to resellers and to original-equipment
manufacturers that repackage and sell it under their own labels.
The powder manufacturers and repackagers may disburse large quantities
of canister powders to distributors who later sell to smaller distributors
and wholesalers, who in turn, supply cans to dealers, gun shops,
shooting clubs, and other retailers. At this point, consumers can
purchase a 1-pound canister of powder for approximately $15 to $20
from a retailer, though the cost per pound can be cheaper if bought
by the keg or acquired through a gun club (National Research Council
who produce smokeless powders for the U.S. military can distribute
it either by selling the powder directly to the military or by selling
them the preloaded ammunition. Powders can also be shipped to U.S.
military subcontractors, foreign governments, or foreign loading
companies for loading into military ammunition (National Research
explosion is the result of energy-releasing reactions, generally
accompanied by the creation of heat and gases (a notable exception
is thermites). A distinguishing characteristic of an explosion is
the rate at which the reaction proceeds. There are low-order and
high-order explosives, based on the speed at which the explosives
decompose. In low-order explosives, the process of decomposition,
called the speed of deflagration or burning, produces heat, light,
and a subsonic pressure wave. (The reaction speed of the deflagrating
material is less than the speed of sound.) In high-order explosives,
decomposition occurs at the speed of detonation, creating a supersonic
shock wave that causes a virtually instantaneous buildup of heat
and gases. Table 1 shows some differences
in low-order and high-order explosives (Bureau of Alcohol, Tobacco
and Firearms 1994; National Research Council 1998; Saferstein 1998).
explosives, rapid deflagration causes the production of large volumes
of expanding gases at the origin of the explosion. The heat energy
from the explosion also causes the gases to expand. When the explosive
charge is confined in a closed container, the sudden buildup of
expanding pressure exerts high pressure on the container walls causing
the container to stretch, balloon, then burst, releasing fragments
of debris to nearby surroundings. It is this fragmented debris that
produces the fatal result following the deflagration of an improvised
explosive device (Saferstein 1998).
The safest and
most powerful low-order explosive is smokeless powder. These powders
decompose at rates up to 1,000 meters per second and produce a propelling
action that makes them suitable for use in ammunition. However,
the slower burning rate of smokeless powder should not be underestimated.
The explosive power of smokeless powder is extremely dangerous when
confined to a small container. In addition, certain smokeless powders
with a high-nitroglycerine concentration can be induced to detonate.
On the other hand, high-order explosives do not need containment
to demonstrate their explosive effects (Saferstein 1998). These
materials detonate at rates from 1,000 to 8,500 meters per second,
producing a shock wave with an outward rush of gases at supersonic
speeds. This effect proves to be more destructive than the fragmented
smokeless powder improvised explosive device, a pipe bomb, is roughly
10 inches long and 1 inch wide and contains approximately ½
pound of powder. The materials used for these devices are cheap
and readily obtainable at commercial establishments. Smokeless powder
is attractive for use in improvised explosive devices, because it
is readily available and has the potential for a powerful explosion
when the powder is placed in a closed container (National Research
Council 1998). Larger explosive devices usually use bulk materials
such as ammonium nitrate and fuel oil, typically purchased in greater
quantity at an even cheaper price.
Many types of
containers are used in the construction of smokeless powder bombs
(National Research Council 1998). Whereas metal pipes are most common,
plastic pipes, cans, CO2 cartridges, and glass or plastic
bottles have been used. These containers are often placed within
larger packages for ease of transport and concealment.
important part of the powder bomb is the initiation system, which
provides the impetus to start the powder burning within its container
(National Research Council 1998). A few examples include cigarettes,
matches, and safety fuses (Scott 1994; Stoffel 1972). Improvised
explosive devices utilizing smokeless powders within a robust container
often include an initiation system, as shown in Figure 2 (Scott
data from the National Research Council on reported actual and attempted
bombings using propellants during the five-year period from 1992-1996,
Table 2 illustrates an average of
653 incidents per year involving the use of black and smokeless
powders. Bombs containing black or smokeless powders were responsible
for an average yearly count of about 10 deaths, 83 injuries, and
almost $1 million in property damage for each of the five years.
Using the National Research Council's data involving devices filled
with black and smokeless powders, Table
3 illustrates the number of actual bombings that caused at least
one death, one injury, or a minimum of $1,000 in property damage,
as well as attempted bombings aimed at significant targets (National
Research Council 1998).
Gradient HPLC analysis of an IMR 700X smokeless powder. Conditions
Restek C-8 Column, 36-80% methanol/water gradient, 1 ml/min,
UV detection at 230 nm. Figure courtesy of Chad Wissinger, Ohio
University Click to enlarge image.
methods for the analysis of smokeless powders have appeared over
the years. These procedures have been extensively reviewed in a
number of recent texts (Beveridge 1998; National Research Council
1998; Yinon and Zitrin 1993). The initial characterization of the
powders is assessed using powder morphology and spot tests. Various
instrumental analytical techniques allow organic additives such
as nitroglycerine, diphenylamine,
ethyl centralite, dinitrotoluene, and various phthalates to be detected
and quantitated. These materials are usually analyzed using gas
chromatography-mass spectrometry (Martz and Lasswell 1983) and liquid
chromatography (Bender 1983; McCord and Bender 1998). Figure 3 illustrates
the analysis of an IMR 700X powder using gradient high performance
liquid chromatography (Wissinger and McCord 2002). More recently,
methods involving capillary electrophoresis have also been shown
to be effective (Northrop et al. 1991; Smith et al. 1999). Fourier
transform infrared microscopy can be used for the identification
of nitrocellulose (Zitrin 1998).
IC Analysis of H414 smokeless powder by Hodgdon. Conditions
Nucleosil Anion IIÒ
1mM DCTA pH 5.2, 1.5 ml/min, UV detection at 205 nm. Click
to enlarge image.
process of manufacturing smokeless powders provides sources of inorganic
ions that are present in postblast residue. These can be analyzed
by ion chromatography. Although not unique to propellants, the presence
of these ions can be used
in forensic analysis to aid in the identification of the unknown
powder. Potassium sulfate, sodium sulfate, potassium nitrate, barium
nitrate, and other salts
may be added during the processing of the powder. Nitrate, sulfate,
hydrogen sulfide, chloride, and nitrite may appear as a result of
the reactions for treating
the cellulose to obtain nitrocellulose (Radford Army Ammunition
Plant 1987). Figure 4 illustrates the analysis of H414 smokeless
powder using ion chromatography. Also documented has been the presence
of various cations found in the residue of smokeless powders after
deflagration (Hall and McCord 1993; Miyauchi et al. 1998).
The wide variety
of chemical components and the different morphologies of smokeless
powders present a challenge for the forensic investigator. Physical
characteristics of partially burned and unburned powder as well
as the organic and inorganic materials that remain must be considered
in the analysis of postblast residue. Although there are many techniques
available for the determination of components in smokeless powder
residue, the various formulations of powders make it necessary to
continue the advancement of existing analyses and to develop new
methods for testing the full range of available smokeless powders.
Bender, E. C.
Analysis of low explosives. In: Forensic Investigation of Explosives.
A. Beveridge, ed. Taylor and Francis, London, 1998, pp. 343-388.
Bender, E. C.
Analysis of smokeless powders using UV/TEA detection. In: Proceedings
of the International Symposium on the Analysis and Detection of
Explosives. U.S. Government Printing Office, Washington, DC,
1983, pp. 309-320.
ed. Forensic Investigation of Explosives. Taylor and Francis,
Bureau of Alcohol,
Tobacco and Firearms, Arson and Explosives Incidents Report (1994).
ATF P3320.4, Department of the Treasury, Washington, DC, 1994.
Hall, K. E.
and McCord, B. R. The analysis of mono- and divalent cations present
in explosive residues using ion chromatography with conductivity
detection, Journal of Forensic Sciences (1993) 38:928-934.
Martz, R. M.
and Lasswell, L. D. Identification of smokeless powders and their
residues by capillary column gas chromatography/mass spectrometry.
In: Proceedings of the International Symposium on the Analysis
and Detection of Explosives. U.S. Government Printing Office,
Washington, DC, 1983, pp. 245-254.
McCord, B. and
Bender, E. C. Chromatography of explosives. In: Forensic Investigation
of Explosives. A. Beveridge, ed. Taylor and Francis, London,
1998, pp. 231-265.
Meyer, R. Explosives.
3rd rev., Weinheim, New York, 1987.
Kumihashi, M., and Shibayama, T. The contribution of trace elements
from smokeless powder to post-firing residues, Journal of Forensic
Sciences (1998) 43:90-96.
Council, Committee on Smokeless and Black Powder. Black and Smokeless
Powders: Technologies for Finding Bombs and the Bomb Makers.
National Academy Press, Washington, DC, 1998.
M., Martire, D. E., and MacCrehan, W. A. Separation and identification
of organic gunshot and explosive constituents by micellar electrokinetic
capillary electrophoresis, Analytical Chemistry (1991) 63:
Ammunition Plant. Processing Manual. Radford, Virginia, 1987.
R. Criminalistics: An Introduction to Forensic Science. 6th
ed., Prentice Hall, Upper Saddle River, New Jersey, 1998.
Scott, L. Pipe
and Fire Bomb Designs: A Guide for Police Bomb Technicians.
Paladin Press, Boulder, Colorado, 1994.
M., Strobel, R. A., and Tontarski, R. E. Systematic identification
of smokeless powders, an update. In: Proceedings of the Third
Symposium on the Analysis and Detection of Explosives. Berghausen,
Fraunhofer Institute fur Chemische Technologie, 1989, Chapter 3,
Smith, K. D.,
McCord, B. R., MacCrehan, W. A., Mount, K., and Rowe, W. F. Detection
of smokeless powder residue on pipe bombs by micellar electrokinetic
chromatography, Journal of Forensic Sciences (1999) 44:789-794.
Explosives and Homemade Bombs. Charles C. Thomas, Springfield,
and McCord, B. R. A reversed phase HPLC procedure for smokeless
powder comparison, Journal of Forensic Sciences (2002) 47:168-174.
Yinon, J. and
Zitrin, S. Modern Methods and Applications in Analysis of Explosives.
John Wiley, Chichester, United Kingdom, 1993.
Zitrin, S. Analysis
of explosives by infrared spectrometry and mass spectrometry. In:
Forensic Investigation of Explosives. A. Beveridge, ed. Taylor
and Francis, London, 1998, pp. 267-314.
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