Priming Compositions

Priming compositions for firearms ammunition are mixtures which, when subjected to percussion, provide a sudden burst of flame that serves to ignite the propellant within the cartridge case. A priming composition must deliver a relatively large volume of hot gases and hot solid particles without the development of a detonating wave.

The ideal priming composition would consist of a cheap, readily available, relatively safe to handle, simple chemical compound of uniform granulation which when subjected to impact would undergo rapid, highly exothermic decomposition. The only compound to even approach these specifications is lead dinitroresorcinate; however, it is far too sensitive. In practice, no single chemical compound meets all the requirements of an ideal primer.

The next most desirable type of priming composition would be a mixture of compounds that, although individually nonexplosive, sensitize each other to ignition and rapid burning. In fact, most priming compositions consist of mixtures of one or more initial detonating agents, with oxidizing agents, fuels, sensitizers, and binding agents. The net effect of the additions is to dilute the initial detonating agent so as to convert its decomposition from detonation into rapid combustion. In some cases a single addition may serve two purposes, for example, antimony sulfide acts as a fuel as well as a sensitizer to friction, and gum arabic acts as a fuel and a binding agent. The oxidizing agents provide oxygen to support combustion of the fuel within the small space of the cartridge case. Fuels are necessary to prolong the combustion long enough to ignite the propellant. The additions may also serve to increase the volume of gases produced per unit weight of priming composition, to prevent the gases from having too high a temperature, and to contribute incandescent solid particles to the decomposition products.

The sensitivity of priming compositions varies, but that of an individual composition can also be varied to some extent by careful control of the granulation of each of the ingredients. Sometimes this is more important than the proportions of the ingredients. Nonuniformity of composition due to physical separation caused by shaking can lead to great variations in sensitivity and even failure to function. The presence of a binding agent prevents such separation as well as fixing the composition in the desired position in the assembly.

The rate of burning, volume of gases, weight of solid particles produced, and the duration of the flame are the major influences on the efficient functioning of a priming composition. For a typical priming composition of 0.15 g, the volume of gases at room temperature and pressure is in the order of 1.5 cm. The percentage of the weight carried as incandescent particles by the hot gases will vary with the composition, but can be in the region of 70%. The incandescent particles are thought to promote ignition by thermal radiation. Flame bursts from various primers were found to have effective durations varying from 400 to 750 microseconds and total durations varying from 650 to 1,500 microseconds.45

Generally speaking small arms primers consist of an explosive, an oxidizer, a fuel, and a frictionator. Other compounds act as sensitizers and binders.

Explosives used include azides, fulminates, diazo compounds, nitro or nitroso compounds, for example, lead or silver azide, mercury fulminate, lead styphnate, TNT, and PETN (which also act as sensitizers).

Oxidizers used include barium nitrate, potassium chlorate, lead dioxide, and lead nitrate.

Fuels used include antimony sulfide (which also acts as a frictionator), gum arabic (which also acts as a binding agent), calcium silicide (which also acts as a frictionator), nitrocellulose, carbon black, lead thiocya-nate, and powdered metals such as aluminum, magnesium, zirconium, or their alloys.

Frictionators used include ground glass and aluminum powder (which also acts as a fuel).

Sensitizers used include tetracene, TNT, and PETN.

Binders used include gum arabic, gum tragacanth, glue, dextrin, sodium alginate, rubber cement, and karaya gum.

The quantity of oxidizer in the mixture is calculated to supply at least enough oxygen for the complete combustion of the primer; otherwise combustion products that are harmful to the firearm could be formed. (The fric-tionators could be regarded as sensitizers as they sensitize the mixture to percussion.) There may be more than one explosive, oxidizer, fuel, and fric-tionator in a single priming composition and sometimes a dye is added as an identifying feature or as an aid in production. Sometimes no single primary explosive is present, the mixture itself being the primary explosive.

In 1805 the Reverend Alexander Forsyth used mercury fulminate as the basis of his primer composition, and from this time the percussion system developed into today's highly reliable, universally used, percussion primer compositions. This development which started in 1805 still continues today, and manufacturers are very reluctant to release details of their compositions.

Consequently, information on primer compositions and the chemical composition of ammunition is both sparse and fragmented in the literature.

It is accepted by most writers that Reverend Forsyth's percussion priming composition was based on mercury fulminate. However, there is some respected opinion which suggests his composition was made up of wax-coated pellets of potassium chlorate mixed with combustible materials, and that it was not until 1831 that mercury fulminate was widely used as the explosive ingredient in primer compositions.46,47

Early priming compositions consisted of mercury fulminate and potassium chlorate along with other ingredients. With the introduction of metallic cartridge cases about 1850, it was found that brass cartridge cases were unsuitable for use with priming compositions containing mercury fulminate as the brass was embrittled due to mercury amalgamation of the zinc. This made the spent cartridge case useless for reloading purposes, and reloading was essential for economic reasons. Initially the use of copper cartridge cases solved this problem. In 1869, Hobbs, by the use of internal varnishing of brass primer cups and brass cartridge cases, made the use of brass and mercury fulminate possible by preventing the direct contact of the brass surface with the primer mix.

Whenever black powder was used as a propellant, a large amount of fouling was deposited on the inside of the barrel. On combustion, black powder produces 44% of its original weight as hot gases and 56% as solid residues in the form of dense white smoke.48 When smokeless powders were introduced between approximately 1870 and 1890, another major problem was encountered. Smokeless powders were harder to ignite than black powder; consequently, larger priming loads were necessary for smokeless powders. Higher pressures were experienced with smokeless powders, and smokeless powders on combustion produced much less fouling than black powder. The relatively clean surfaces remaining in the barrel interior after the combustion of smokeless powder became rusted, even when the gun was cleaned immediately after use.

The cause of the rusting was traced to the potassium chlorate used in the priming composition. Potassium chloride, formed after the combustion of potassium chlorate, was deposited inside the barrel; it then attracted atmospheric moisture and caused rapid rusting of the barrel interior. Gun cleaning mixtures were organic in nature and did not dissolve the potassium chloride; consequently, despite cleaning immediately after use, salt particles trapped in the rifling and surface imperfections of the metal still caused rusting. Water proved to be efficient at removing all traces of the salt; however, it was then necessary, and very difficult, to ensure that all the water was removed from the gun; otherwise the water itself would cause rusting. The heavy residue left after the combustion of black powder substantially protected the metal surfaces from the effects of the salt, and to some extent from the effects of metallic mercury released after combustion of the primer.

The problems associated with the use of mercury fulminate and potassium chlorate led to a search for suitable alternatives, and the chemical reactions occurring within the cartridge case and the firearm were intensively studied. The objective of the study was to produce a satisfactory priming composition which was both noncorrosive and nonmercuric (NCNM).

As a result of the need to reuse spent cartridge cases for economic reasons, there has been no mercury in U.S. military small arms primers manufactured since 1898. It was used to a later date (about 1930) in certain U.S. commercial primers. In 1898 the U.S. military adopted a nonmercuric primer composition, coded H-48, for use in the .30 Krag cartridge. The primer composition was:

Potassium chlorate 49.6%

Antimony sulfide 25.1%

Sulfur 8.7%

Glass powder 16.6%

During World War I the nonmercuric primer mixture used was:

Frankford Arsenal FH-42 (1910) Potassium chlorate 47.20%

Antimony sulfide 30.83%

Sulfur 21.97%

It was discovered in 1911 that thiocyanate-chlorate mixtures were sensitive to impact, and this led to the Winchester Repeating Arms Company's 35-NF primer composition:

Potassium chlorate 53%

Antimony sulfide 17%

Lead thiocyanate 25%

After a batch of damp sulfur and/or impure potassium chlorate (polluted with potassium bromate) caused "dead" primers in millions of rounds of ammunition with Frankford Arsenals FH-42 primer mix, this primer composition was abandoned. Frankford Arsenal adopted the Winchester Repeating Arms Company's 35-NF primer mix which was then standardized as FA-70 and was used in 0.45 ACP and .30-06 ammunition throughout World War II and into the 1950s.

At this time a typical .22" caliber rimfire primer composition was the United States Cartridge Company's "NRA" which was:

Potassium chlorate 41.43%

Antimony sulfide 9.53%

Copper thiocyanate 4.70%

Ground glass 44.23%

It would appear that the Germans were approximately 23 years ahead of the Americans in the production of noncorrosive primers, despite the fact that the German compositions were published in the open literature. This may have been due to patent rights.

The first noncorrosive primer was produced by the German firm of Rhe-inische-Westphalische Sprengstoff AG (RWS) in 1891:

Mercury fulminate 39%

Barium nitrate 41%

Antimony sulfide 9%

Picric acid 5%

Ground glass 6%

(Barium nitrate replaced potassium chlorate.)

In 1910 the same firm produced the following .22" caliber rimfire priming composition:

Mercury fulminate 55%

Antimony sulfide 11%

Barium peroxide 27%

The Swiss Army had also been using a noncorrosive primer mix since 1911:

Mercury fulminate 40%

Barium peroxide 25%

Antimony sulfide 25%

Barium carbonate 6%

Ground glass 4%

It was not until 1927 that the first American commercial noncorrosive primers appeared on the market. Some of these are as follows49:

Remington Winchester Peters

Kleanbore Western Staynless Rustless

Mercury fulminate % 44.50 40.79 41.06 38.68

Barium nitrate % 30.54 22.23 26.03 9.95

Lead thiocyanate % 4.20 8.22 5.18

Ground glass % 20.66 28.43 26.66 24.90

Up to this time primers had fallen into three categories: mercuric and corrosive, nonmercuric but corrosive, and mercuric but noncorrosive. Because of the disadvantages of mercury fulminate and potassium chlorate the main objective of primer development was to produce a primer with satisfactory ignition properties without the use of these two compounds. An early NCNM priming composition used copper ammonium nitrate to replace mercury fulminate, and potassium nitrate to replace potassium chlorate. The composition was:

Copper ammonium nitrate 30% to 40%

Potassium nitrate 42% to 25%

Aluminum 18% to 28%

The first practical NCNM primer mixture with satisfactory ignition properties and good shelf life was produced by RWS in 1928. This type of primer was given the general name of "Sinoxyd" (Sinoxide/Sinoxid) and has the following general composition:

Lead styphnate Barium nitrate Antimony sulfide Lead dioxide Tetracene Calcium silicide Glass powder

25% to 55% 24% to 25% 0% to 10% 5% to 10% 0.5% to 5% 3% to 15% 0% to 5%

(Lead styphnate replaced mercury fulminate.)

This was the forerunner of all modern NCNM priming compositions. With very few exceptions, U.S. commercial primers became noncorrosive about 1931 but because of stringent U.S. government specifications for military ammunitions, which could not be met by the earlier versions of the new

NCNM primer mixtures, it was not until the early 1950s that U.S. military ammunition became noncorrosive. This was because early NCNM commercial priming mixtures suffered erratic ignition and unsatisfactory storage stability, and as large quantities of small arms ammunition are stored as a war reserve, military ammunition must have unquestioned reliability and storage stability.

In the United Kingdom both commercial and military ammunition used primers that were both mercuric and corrosive, until the gradual changeover to NCNM primers which was completed during the mid-1950s and early 1960s.

The explosive ingredient in Sinoxyd-type primers is lead styphnate (lead trinitroresorcinate), which is very sensitive to static electricity, and fatalities have resulted from handling the dry salt. Preparation of the pure salt is difficult, and many patented preparations, including basic modifications, exist. Some claim special crystalline forms and/or reduced static electricity hazard. Explosive ingredient substitutes for lead styphnate were sought that would be easier to make and safer to use. These included lead azide, diazonitrophenol, lead salts of many organic compounds, complex hypophosphite salts, pic-rate-clathrate inclusion compounds, and pyrophoric metal alloys.

In 1935 lead azide was patented for use in priming mixtures in the following mix:

Lead azide

12%

Barium nitrate

23%

Antimony sulfide

20%

Calcium silicide

10%

Tetracene

3%

Lead dioxide

20%

Lead thiocyanate

12%

In 1939 a primer mixture was patented that was identical to Sinoxyd except that diazonitrophenol was substituted for lead styphnate. Heat, humidity, and copper have a detrimental effect on diazonitrophenol and it is no longer used in primer mixes.

Normal lead styphnate has one lead atom per formula unit, whereas the basic form has two. A priming mixture using basic lead styphnate was patented in 1949:

Basic lead styphnate 40%

Barium nitrate 42%

Antimony sulfide 11%

Nitrocellulose 6%

Tetracene 1%

Other substitutes for lead styphnate included lead salts of many organic compounds, none of which gained widespread acceptance.

It was not until 1954 that preparation of the pure compound, normal lead styphnate hydrate, was accomplished. Up to this time the impure salt (~93%) was used extensively.

Complex hypophosphite salts have been used successfully as substitutes for both lead styphnate and tetracene. A 1939 patent gives the following composition:

Lead styphnate 33%

Calcium hypophosphite 7%

Lead nitrate 14%

Lead thiocyanate 10%

Barium nitrate 16%

Glass powder 20%

When wet with water a reaction occurs between the calcium hypophosphite and the lead nitrate, producing a shock-sensitive nonhygroscopic compound which incorporates both oxidizer and fuel.

In 1944 a patented rimfire priming mix included a triple salt, that is, basic lead styphnate-lead styphnate-lead hypophosphite, in the following mix:

Triple salt 50%

Lead nitrate 30%

Glass powder 20%

In 1955, patents were issued for a nontoxic, lead-free, rimfire priming mixture which used the double salt, ferric styphnate-ferric hypophosphite, and for a glassless rimfire priming mixture which used a triple salt, potassium styphnate-lead styphnate-lead hypophosphite, in the following unusual mixture:

Triple salt 10%

Lead styphnate 36%

Barium nitrate 50%

Tetracene 4%

About 1949 Frankford Arsenal manufactured an unusual priming mixture known as the P-4 primer (coded FA675):

Stabilized red phosphorus 18% Barium nitrate 82%

Although this was a simple, relatively safe mixture, and was a satisfactory primer, it was discontinued after a very short period because of two major disadvantages. It was shown that copper, bismuth, silver, iron, and nickel increased the oxidation rate of red phosphorus to acidic compounds. Primer cups had to be zinc plated to prevent contact with copper. The red phosphorus had to be of high purity, and it was necessary to remove the major impurities (iron and copper) from commercial red phosphorus before use, and to coat the purified material with up to 7.5% aluminum hydroxide which inhibited oxidation.

Although the P-4 primer was only in use for approximately 1 year, it was further improved in 1961 by coating the stabilized red phosphorus with PETN, RDX (cyclotrimethylenetrinitramine), or TNT giving the following primer mix:

Stabilized red phosphorus 25%

However, red phosphorus primers never achieved widespread use, presumably due to manufacturing difficulties.

In the early 1960s important advances were made in the development of safer, easier to make, cheaper, and better substitutes for lead styphnate, which had been the main explosive ingredient in successful NCNM priming mixtures up to this time.

In 1962 Kenney applied for patents on many complex, basic lead pic-rate-clathrate inclusion compounds which did not have the static electricity hazard of lead styphnate. Of 44 compounds listed in his patent, monobasic lead picrate-lead nitrate-lead acetate was preferred for primers, although monobasic lead picrate-lead nitrate-lead hypophosphite; dibasic lead pic-rate-lead nitrate-lead acetate; and monobasic lead picrate-lead nitrate-lead acetate-lead hypophosphite were also suitable. Glass was thought to damage the bore of the firearm and was considered by some to be undesirable. A glassless rimfire mixture was:

Any of the previous complex salts 46% Barium nitrate 50%

Tetracene 4%

In 1962, Staba applied for patents on a double salt, lead nitroaminotet-razole-lead styphnate, which became known as stabanate, and had much better thermal stability than lead styphnate. A primer mix claimed to be superior to the lead styphnate-based equivalent was:

PETN, RDX, or TNT Barium nitrate

Stabanate Barium nitrate Antimony sulfide

Tetracene Aluminum

In 1966, Staba applied for a patent on certain forms of carbon that exhibit conchoidal fracture (very sharp, jagged concave edges) when shattered. A rimfire primer mix was:

An interesting stage in the development of primer mixes was the use of pyrophoric metal alloys, first patented in 1936 and improved in 1964. These rare earth alloys, as used in cigarette lighter flints, give a shower of sparks when lightly scraped. A typical pyrophoric alloy is "misch metal," which has the following approximate composition: cerium 50%, lanthanum 40%, other rare earth elements 3%, and iron 7%.

There are many patents listed in which the pyrophoric alloy replaces the function of both lead styphnate and tetracene. One of the most sensitive mixtures was:

Misch metal/magnesium (80/20 alloy) 50%

Barium nitrate 20%

Lead dioxide 10%

Zirconium powder 20%

Lead styphnate

Stabanate

Barium nitrate

Tetracene

Karaya gum

Ground anthracite coal

Another of Staba's primer mixes:

Stabanate

Tetracene

PETN

Aluminum

Nitroaminoguanidine

Karaya gum

Gum arabic

Pyrophoric alloy primer mixtures never achieved widespread use, presumably because of their lack of sensitivity to percussion.50

There are hundreds of patents issued for priming compositions, a fact that illustrates the considerable experimentation in this area. Examples of some of these are:

Mercury fulminate

20% to 50%

Barium nitrate

19% to 45%

Lead chromate

2% to 20%

Lead sulfocyanide

3% to 25%

Zirconium powder

2% to 30%

Glass powder

30%

Basic lead trinitroresorcinol

27%

Lead dinitrophenylazide

13%

Potassium nitrate

30%

Antimony trisulfide

7%

Ground glass

23%

Mercury fulminate

33%

Thallium nitrate

40%

Cobalt nitrate

10%

Antimony trisulfide

17%

Potassium chlorate

85%

Asbestos fiber

1.5%

Nitrotoluol

4.5%

Petroleum gel

8.5%

Castor oil

0.5%

Potassium chlorate

48% to 53%%

Potassium ferrocyanide

33/% to 36%

Glass powder

13/% to 16%

Tetracene

1% to 4%

Diazonitrophenol

12% to 18%

Barium nitrate

25% to 40%

Antimony trisulfide

8% to 18%

Lead peroxide

15% to 25%

Calcium silicide

8% to 20%

Tetrazene

4% to 7%

Diazonitrophenol Basic lead azide Barium nitrate Lead peroxide Ground glass

15% to 20% 6% to 12% 20% to 30% 12% to 20% 20% to 28%

Lead azide 20 to 25 oz.

Powdered glass 20 to 25 oz.

Flake aluminum 6 to 8 oz.

Barium nitrate 35 to 38.5 oz.

Trinitrotoluol 0 to 25 oz. Canada balsam or cellulose acetate 0 to 2.5 oz.

m-Toluenesulfomethylamide 0 to 1 oz.

Mercury fulminate 65.0 g

Barium nitrate 22.0 g

Antimony sulfide 11.0 g

Hexogene 15.5 g

Barium carbonate 1.5 g

Gum arabic 30 g

Phosphorus sulfide 15 g

Magnesium carbonate 12 g

Calcium carbonate 5 g

Potassium chlorate 60 g

Mercury fulminate 37.5%

Potassium chlorate 37.5%

Antimony sulfide 25.0%

Mercury fulminate 25.9%

Potassium chlorate 48.2% Antimony sulfide 3.7%

Ground glass 22.2%

Mercury fulminate 19.1%

Potassium chlorate 33.3%

Antimony sulfide 42.8% Sulfur 2.4% Mealed powder 2.4%

Lead trinitroresorcinol Tetracene

Barium nitrate Lead oxide

Calcium silicate Powdered glass

Despite the search for alternatives to lead styphnate and the considerable experimentation with primer compositions, in the United Kingdom and the United States, the vast majority of modern ammunition contains Sinoxyd type primers with lead styphnate and barium nitrate together typically making up 60% to 80% of the total weight. They also contain some of the following:

Antimony sulfide Tetracene Calcium silicide Lead dioxide Aluminum powder Ground glass Lead hypophosphite Lead peroxide Zirconium Nitrocellulose Pentaerythritol tetranitrate Gum type binder

Composition control is very stringent and ingredients are of analytical reagent quality.

Mercury fulminate/potassium chlorate-based primer compositions are currently manufactured by some Eastern Bloc countries, although they also manufacture compositions based on lead styphnate.

Examples of some modern U.S. priming mixtures are51:

Normal lead styphnate 36%

Barium nitrate 29%

Antimony sulfide 9%

Lead dioxide 9%

Tetracene 3%

Zirconium 9%

Pentaerythritol tetranitrate 5%

Basic lead styphnate

39%

Barium nitrate

40%

Antimony sulfide

11%

Tetracene

4%

Nitrocellulose

6%

Normal lead styphnate

37%

Barium nitrate

38%

Antimony sulfide

11%

Tetracene

3%

Pentaerythritol tetranitrate

5%

Nitrocellulose

6%

Normal lead styphnate

41%

Barium nitrate

39%

Antimony sulfide

9%

Calcium silicide

8%

Tetracene

3%

Normal lead styphnate

43%

Barium nitrate

36%

Calcium silicide

12%

Tetracene

3%

Lead peroxide

6%

Examples of some modern U.K. priming mixtures are52:

Lead styphnate

35%

Tetracene

3%

Lead peroxide

15%

Barium nitrate

47%

Lead styphnate

46%

Tetracene

4%

Barium nitrate

25%

Antimony sulfide

20%

Aluminum

5%

Lead styphnate

44.2%

Tetracene

3.3%

Barium nitrate

20.4%

Ground glass

25.0%

Lead hypophosphite

Lead styphnate Tetracene

Lead peroxide Barium nitrate

Antimony sulfide Calcium silicide

An interesting and extremely successful primer innovation was introduced by Eley and is known as Eleyprime. Instead of using lead styphnate, with its inherent safety and processing difficulties, Eley uses calculated amounts of lead monoxide and styphnic acid which are much safer to process. At the end of the processing stage a drop of water is added to each individual primer which initiates a chemical reaction between the lead monoxide and the styphnic acid to form lead styphnate. The final product when dry is no different from a conventional primer.

In conventional ammunition lead, antimony, and barium are emitted when the ammunition is discharged. These three elements are undesirable from a health viewpoint and pose a major problem for firearms instructors in indoor firing ranges, as they are exposed to an unhealthy environment each working day. To solve this problem Dynamit Nobel AG developed a nontoxic primer composition called Sintox. Lead styphnate is replaced by 2-diazo-4,6-dinitrophenol (diazole) and the barium nitrate and antimony sulfide are replaced by a mixture of zinc peroxide and titanium metal powder.

The Sintox primer mixture contains tetracene, diazole, zinc peroxide/ titanium powder, and nitrocellulose ball powder.53 The use of this primer coupled with a totally jacketed bullet (base also enclosed) entirely eliminates the health hazard problem.

CCI and Fiocchi produce lead free primers, Fiocchi substituted diazole for the lead compound, and CCI uses diazole, manganese(iv) oxide, and aluminum.54

The use of titanium as a replacement for calcium silicide in conventional Sinoxyd primers is being investigated by Dynamit Nobel. Since they were introduced, lead free primers have improved to the extent that their performance rivals that of conventional lead-containing primers which they will probably replace in the near future.

Primer mixtures can be divided today into six categories: (a) mercuric and corrosive, (b) mercuric and noncorrosive, (c) nonmercuric and corrosive, (d) nonmercuric and noncorrosive, that is, Sinoxyd type, (e) Sintox type, that is, lead free, and (f) miscellaneous (unusual priming compositions).

Two-component primer compositions (based on lead and barium compounds) are more common than three-component types (based on lead, barium, and antimony compounds) in rimfire primed ammunition. However, three-component rimfire primers are far from rare. Some manufacturers use both two- and three-component primers in their range of rimfire ammunition.

Primers are not used exclusively for firearm ammunition, but have other uses which include blank cartridges, flares, flare trip wires, mortars, pyrotechnic cartridges, hand grenades, rocket-propelled grenades, ejector seat mechanisms, jettison devices, and other larger ammunition components.

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Responses

  • andrea
    What is a priming composition?
    4 years ago
  • donnamira
    What is the chemical mixture for pistol primer?
    3 years ago
  • Savanna
    What is composition of .22 primer?
    2 years ago
  • laura sal
    Is red phosphorus found in rimfire primer composition?
    1 year ago
  • diamond rumble
    What is composition of prming mixture?
    8 months ago
  • jenna
    How is zink used in world war ammunition?
    7 months ago
  • senja
    What is the chemical used in eley primers?
    7 months ago

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