Primers: An Important Factor in Precision Reloading

Pistol primers should not be used in rifle cases since they will seat too deeply as in the case on the left. Center case shows proper seating depth while high primer on the right will give poor ignition and possible slam-fire in an autoloader.

Pistol primers should not be used in rifle cases since they will seat too deeply as in the case on the left. Center case shows proper seating depth while high primer on the right will give poor ignition and possible slam-fire in an autoloader.

PRIMER EVOLUTION
Match locks, equipped with a slow-smoldering fuse made of chemically treated rope called a “match,” would burn out in damp weather and could be blown out by wind. Wind and damp were the enemies of flintlocks that could blow the priming charge out of the funnel-shaped pan or saturate it with moisture to the point where it would not catch fire. Rust and powder fouling in the tiny tube that connected the charge in the pan to the propelling charge in the barrel often prevented a successful firing with only the priming charge burning.

The expression “a flash in the pan” is still used to describe a person or enterprise that shows promise, but fails to get past a good beginning. Under the best of circumstances, the flintlock system gave only reasonable reliability. A small piece of cut flint held in the jaws of the hammer struck a steel cover on the pan called a frizzen, knocking it open and scraping the inner side to throw sparks into the powder charge in the pan.

In terms of speed it was slow. Anyone who has seen a flintlock fired is familiar with the puff-boom! sound of the report as the priming charge burns with a one-beat pause before the propelling charge fires. History is filled with untold numbers of targets, animal and human, who have ducked to safety during that beat, which was sometimes two beats if the day was damp and the tube to the barrel a bit clogged.

Berdan (left) and Boxer primer pockets show the differences in the systems. The ease of reloading made the Boxer primer standard in the U.S. (Photo courtesy CCI.)
Berdan (left) and Boxer primer pockets show the differences in the systems. The ease of reloading made the Boxer primer standard in the U.S. (Photo courtesy CCI.)

Explosives such as fulminate of mercury and mixtures including potassium chlorate that detonated when crushed or struck, were discovered late in the 18th century. After attempts to use them as substitutes for gunpowder failed, they received little attention until the early 19th.

The breakthrough to improved ignition was made by a Scottish Presbyterian minister, hunter, shooter and gun buff – Reverend Alexander Forsythe — who was the first to come up with the idea of using these detonating explosives to ignite propelling charges in firearms. He received a patent in 1807 for a system that did away with the priming pan on the flintlock and filled the tube leading to the barrel with a percussion explosive made of sulphur, potassium chlorate and charcoal.

A metal pin was inserted on top of the explosive which caused it to detonate when struck by the gun’s hammer. The ignition was far faster and more certain than the flintlock. Forsythe improved his design by attaching a small iron bottle containing a supply of percussion explosive to the side of the lock. The bottle could be tipped or turned to deposit a small pellet of explosive on a touch hole which would be struck by the hammer. The system worked effectively. However, it involved having a small iron bottle filled with explosive very close to the firing point and to the face of the shooter. I have never encountered a report of an accident with a Forsythe lock, but if one happened, it would almost certainly have been fatal.

The superiority of the Forsythe system was soon recognized and dozens of priming systems were introduced including percussion wafers, tubes and strips of paper caps, much like those used in toy cap pistols.

The most successful was the percussion cap invented in about 1814 by Joshua Shaw — a British subject who emigrated to America. Shaw’s system featured a small steel cup, about the size of a modern large pistol or large rifle primer. The closed end contained the explosive held in place by a tinfoil cover then sealed with a drop of lacquer. This made it waterproof as well as damp proof. The cap was fitted on a short iron nipple, hollow in the center, screwed into the breech of the barrel.

This allowed the fire to enter the chamber of the gun. Shaw came to America in 1814 and began perfecting a lock to work with his invention. Shaw caps were on the market by 1821 and were soon adapted to sporting guns. Improvements were made by changing the cap metal to pewter and later copper. Similar caps were in use about the same time over most of Europe. The percussion cap was not adopted by the U.S. military until after the Mexican War. The military thinking at the time was that the percussion cap was yet another component the soldier had to carry and not reusable in the manner of a gun flint.

Percussion caps made the Colt revolver a practical reality, but the shortcomings of this system became apparent when repeating rifles were made using this system. A “flash over” from one chamber to the next would occasionally send a bullet coasting by the side of the gun. With a handgun this was of little consequence since it was a one-hand weapon. With the rifle or shotgun such an event often amputated the fingers or thumb of the hand supporting the fore-end of the weapon. Revolving rifles, not surprisingly, did not gain much popularity.

Breechloading arms, other than revolvers, using percussion ignition did not fare much better mainly because no one was able to come up with an effective means of engineering a gas-tight seal at the breech closure.

Not surprisingly the first really successful breechloaders and successful repeating arms, other than revolvers, required a self-contained, self-primed cartridge. The step to the rimfire cartridge from the percussion cap was a small but logical evolution. George Morse placed a percussion cap in the head of a metal cartridge using a hairpin-shaped anvil inside the case to fire it. Hiram Berdan shortened the hairpin to a tiny knob, while Edward Boxer placed a tiny anvil inside the cap.

COMMENT