Primers: An Important Factor in Precision Reloading


The RCBS APS primer feeder uses plastic strips instead of the conventional stacking tube, reducing the hazard of sympathetic detonation. (Photo courtesy RCBS.)

The RCBS APS primer feeder uses plastic strips instead of the conventional stacking tube, reducing the hazard of sympathetic detonation. (Photo courtesy RCBS.)

Modern primers of the lead, barium and antimony type fulfill all the necessary criteria for good ignition. The binders are now stable and remain stable for long periods under normal “house” storage conditions where temperatures are under 125 degrees Fahrenheit and moisture is kept at a reasonable level. The newest are the “lead free” primers of tetracene. These, however, are not presently sold as reloading components since the production demand is for finished ammunition. The primary use of such primers is in handgun ammunition to be fired in indoor ranges where airborne lead could present a health hazard.

Because of the difficulty of reloading them, cartridges using Berdan primers and the Berdan primers themselves have virtually disappeared from the U.S. Foreign cartridges often still use this type of priming and can only be reloaded with Berdan primers.

Any attempt at “converting” Berdan cases to Boxer priming by drilling them in some manner will not work and such attempts are very dangerous since they will greatly enlarge the flash hole and may damage the web. At best such conversions give uneven ignition; at worst they can raise pressures to dangerous levels by causing too rapid a burn of the powder charge. The only current source for Berdan primers and Berdan decapping equipment is The Old Western Scrounger.

A modern Boxer primer differs little in structure from those made over a century ago. It is a brass cup containing the priming compound. A paper seal keeps the compound in the cup and is held in place by the metal anvil made of harder brass. A better understanding of metallurgy and chemistry has resulted in a more uniform primer as well as ones which are specifically tailored to a particular type of cartridge.

Primers for pistols and rifles come in two basic sizes: “small” (.175″ diameter) and “large” (.210″ diameter). There is a .317″ primer manufactured by CCI used only in the .50 Browning machine gun cartridge – loaded by a few shooters using extra heavy bench-rest rifles in this caliber.

Small pistol primers are used in such calibers as 25 and 32 caliber handgun ammunition while the large size are used in 41, 44 and 45 caliber handguns. Large pistol primers are also made in a “magnum” variant. These are for large capacity cases using slow-burning powders that are harder to ignite and require a longer-burning, hotter primer to draw the most uniform and complete burning from these powders.

Rifle primers are made in the same two diameters as pistol primers and are designated “small” and ”large” although they are slightly higher to fit the deeper pocket in the rifle cartridge case. For this reason pistol primers should not be seated in rifle cases since they will seat too deeply and will thus often give uneven ignition. Rifle primers contain more priming compound than pistol primers since they have to ignite more powder in larger capacity cases. If you are loading both handgun and rifle ammunition, care must be taken not to mix rifle and handgun primers.

If rifle primers are seated in pistol cases they will not fit properly. They can also raise pressures to the danger point. Pistol primers tend to burn cooler, and produce more of a flame type of explosion — good for igniting fast-burning pistol powders. Rifle primers burn longer and hotter. They often contain metallic elements such as aluminum which create burning sparks that are blown forward into a charge of slower-burning powder.

This separates, the grains thus setting the charge on fire in a number of places at once to achieve an even burning of the charge. This explosive quality is known as “brisance.” Magnum rifle primers have still more compound, burn longer and hotter and are used in very large-capacity cases such as the 458 Winchester Magnum. Companies such as CCI also market a “bench rest” rifle primer.

This is simply a standard rifle primer, but made to very strict tolerances assuring the reloader that each primer in a given lot will have a very precisely measured amount of compound and that the diameter and hardness of all components are within very strict tolerances. These premium-quality primers give very even ignition needed for the exacting demands of the expert, competition target shooter.

Shotshell primers have special characteristics needed to work properly in modern, plastic shotshells. Early shotshells were made of brass and were generally of a rifle-type of construction. They used rifle-style primers. Modern shells are of a composite construction with a metal head surrounding a paper, now primarily a plastic body. Inside is a base wad made of plastic or compressed paper.

Shotshells have unique ignition problems. As the mouth of the shell becomes worn and softened with repeated reloading the opening of the crimp becomes progressively easier. Modern shotgun powders require a certain amount of pressure and confinement to function properly. This decreases as the crimp softens. For proper ignition, the powder requires a very high temperature over a longer than usual burn time but without the brisant quality of the magnum rifle powder which would tend to blow the crimp open before much of the powder was ignited. A shotshell primer produces what is often referred to as a “soft ignition.”

Because of the design of modern shotshells, the primer is held in a large, longer than normal housing called a “battery cup” which extends well into the base wad so the flame issuing from the primer mouth will not be inhibited by any part of the wad and can direct its full blast into the powder charge.

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