The flintlock and all of its predecessors had an external pan that held the priming charge in a position where sparks (or the match in primitive arms) could reach the charge. The vent was a required feature yet left a hole in the combustion area of the barrel. After the flame from the priming charge ignited the main charge, gases and other combustion by-products would escape through the vent. This reduced the amount of gas available to push the projectile, allowed moisture into the main charge, and exposed the shooter and those nearby to particulate residue that could injure eyes and skin. Combined with the fragile nature of pan priming, the vent forced a technology leap to achieve a military weapon that could handle a wider range of environmental conditions and more efficiently use the propellant’s stored energy.
Modern firearm barrels are tubes open at both ends except when ready for firing. Chemical ignition led to the development of designs for temporarily sealing one end of the barrel.
Chemical initiation overcame the problem of waterproofing and improved the speed and ease of loading. Chemical initiators for cartridges are percussion-sensitive compounds or mixtures of materials. Alone, these mixtures will not produce sufficient heat or sparks for igniting propellants, but will do so in combination.
The first widely used chemical initiators contained mercury fulminate or potassium chlorate in combination with oxidizers. As a group, these mixtures were called fulminating powders. Although knowledge of their properties dates to the beginning of the eighteenth century, their full benefits for firearm ignition were not realized until 1793. A Scottish Presbyterian minister, the Reverend Alexander John Forsyth (1768-1843), was an avid hunter, enjoyed repairing firearms, and dabbled in chemistry. He began experimenting in 1793 with pellets of fulminating powder placed on a tube that could be struck by the firearm’s hammer. The fulminate exploded, and its flame passed through the tube into the main propellant charge. History credits Forsyth with fabricating the first gunlock to use fulminating powder around 1812.
Forsyth continued to work with fulminate pellets. His lock systems evolved into a pivoting magazine holding multiple pellets that fell on the ignition tube as the magazine was rotated. The Forsyth system was used in high-grade sporting arms, but was considered too expensive and delicate for widespread military application.
A number of inventors saw the usefulness of fulminate for firearm ignition. A variety of fulminate holders were used, including tapes containing multiple pellets (nearly identical to toy gun roll caps), discs, and tubes. Tubes containing fulminate were an invention of noted British gun maker Joseph Manton. They were about 5/8" in length and were installed for each shot at a right angle to the bore in flint-fired arms (in a location roughly corresponding to the vent). The hammer struck the side of the tube, igniting the fulminate and subsequently the main charge.