Priming compounds are highly explosive chemical that, when struck by the firing pin , or the hammer on a weapon will explode with great violence and cause a fire to ignite the propellant.
The explosive chemical is frequently combined with other chemicals that help in the creation of flames, fuel that can increase the length and temperature of the flame , and ground glass as an abrasive to assist in the initial ignition of the explosive.
In the realms of forensic science finding of 209 primers discharge residue on the hands could provide vital evidence as to whether a person is recently firing a weapon. It is essential to have a basic knowledge of the background of primers, their composition, and the manufacturing of primers to make the most of gunshot residue analysis (GSR).
A brief history of the priming compounds
Mercury fulminate was first priming chemical. It was employed in the Forsythe perfume bottle priming system that was introduced in 1806. This compound is highly sensitive and liable to spontaneously explode without explanation. This is why the Forsythe scent bottle, which required a considerable quantity of this chemical to be placed in a container that was carried that was placed on the side of the pistol, did not gain much popularity.
In 1807, Forsythe introduced an encapsulation compound that had a formula consisting of 70.6 parts potassium chlorate 17.6 parts sulfur, and 11.8 parts of charcoal. Whilst this was somewhat more durable than mercury fulminate was terribly destructive.
Joshua Shaw introduced the first percussion cap in 1814. It was a small metal cup that contained the priming mix and was attached to a nipple at back of the barrel. Because of the insanity of pure mercury fullminate, it was overtaken in 1818 by a mixture consisting of mercury fulminate, potassium cyanate, sulfur and charcoal. The resulting residues from this mixture were, however, extremely corrosive, requiring cleaning the gun promptly after firing.
Dreyse created the "needle gun" in 1828. It had a paper cartridge , with propellant in it and a primer cup. The firing pin of the gun was a long thin needle which entered the case and struck the primer inside. The primer cup contained a mix of potassium chlorate and antimony sulfide.
The purification of the mercury-fulminate can lead to an inert compound. In 1873, the US common military priming compound comprised mercury, potassium chlorate and glass dust. The principal drawbacks to the mixture were that (i) the mercury caused the brass cartridge cases hard that caused the case to fail upon firing, as well as high-pressure gas leakage out of the weapon's breech. (ii) following firing the gun, the potassium chlorate left extremely corrosive residues in the bore of the gun.
Non-mercuric, non-corrosive primer composition
These issues led to development of a non-mercuric, corrosion-resistant primer. Initial attempts focused on using potassium chlorate as the principal ingredient. Potassium chlorate is however, a very unstable substance and is deliquescent, meaning that it absorbs water from the air.
It also creates potassium chloride upon decomposition that is also deliquescent, and extremely corrosive to the bore of the weapon.
In the days prior to World War I, it was discovered that thiocyanate/chlorate mixtures were prone to impacts. But, they suffered the same issues as straight chlorate 209 primers and leave behind corrosive residues following firing.
The German RWS company RWS was the first company to substitute potassium chlorate for barium nitrate. The principal explosive ingredient led styphnate was used to make the first primer that was free of rust. This was patented in 1928 and was marketed under the name Sinoxid.
The first true non-corrosive, non-mercuric (NCNM) primers were commercially manufactured in America between 1935 and 1938. These, however, didn't meet the strict US government requirements regarding storage, misfires, others, and so on. Military ammunition continued to use the old corrosive chlorate mixtures right through World War II.