The Primer

The Primer

Along with the evolution of the metallic cartridge case and more efficient propellants, some reliable method of igniting the package was required. This is the job of the primer. Today’s primers are essentially a metallic cup containing an explosive mixture that serves to ignite the main powder charge. The modern primer traces its history back to the “detonating powder” developed in 1805 by Reverend Alexander Forsyth. Forsyth’s compound utilized a mixture of fulminate of mercury and potassium chlorate, offering a more convenient and reliable alternative to the flintlock ignition system. This was no small accomplishment, considering that the flintlock ignition system had dominated the firearms world for over two hundred years. Credit for the invention of the percussion cap is somewhat obscure, with claims having been made by a long list of English, French, German and Swiss experimenters. Joshua Shaw, an English born American immigrant, is generally given credit for having developed the first metallic percussion cap in 1814. Shaw’s percussion caps used an explosive mixture of fulminate of mercury, chlorate of potash, and ground glass contained in a small metallic cup. In use, this cup was placed on a nipple beneath the firearms hammer. When the trigger was pulled, the hammer’s blow caused the percussion cap to detonate. This sent a jet of hot gases through a flash hole in the nipple, igniting the primary charge of black powder, and discharging the ball out the muzzle of the firearm. In a modern cartridge, each of these different components is still present, albeit in a single, self-contained unit. The percussion cap has since become the primer. The nipple, originally part of the firearm, is now located either in the case (Berdan) or the primer in the form of the anvil (Boxer). The chamber walls, which held the powder, have now been supplemented with a fixed cartridge case.

Boxer or Berdan?

Today, there are two basic priming systems in use worldwide for metallic cased small arms ammunition. Designated as either Boxer or Berdan, they are named after their respective designers. In a perverse quirk of fate, the priming system used in England and throughout much of the rest of the world was developed by an American, Col. Hiram Berdan. The predominant priming system used here in the U.S. was invented by an English ordnance officer, Col. Edward Boxer. The two systems are not at all interchangeable, and must not be confused.


The primary difference between the two is the placement of the anvil, the point against which the priming compound is crushed. In the Boxer system, the anvil is a separate piece affixed into the primer’s cup, and bottoming out in the primer pocket when the primer is seated. The Berdan system utilizes an integral anvil, formed into the base of the primer pocket. Additionally, Boxer primed cases utilize a single, fairly large, centrally located flash hole, making them eminently suitable for reloading. Berdan primed cases, on the other hand, normally have two or more smaller flash holes, located at various points around the anvil. This makes it impossible to decap Berdan cases as easily and efficiently as Boxer primed cases. While Berdan brass can be reloaded, decap-ping the cases is much more time consuming, and requires specialized equipment that is not commonly available. Essentially, reloading Berdan cases is not worth the effort if Boxer primed cases can be purchased or formed.

The Berdan system has seen little use here in the U.S., and is rarely encountered in anything but imported surplus foreign military ammunition. One exception to this is the CCI Blazer® line of aluminum cased, Berdan primed cartridges. In addition to their readily identifiable aluminum cases, Blazer cases are prominently headstamped “NR” to indicate their non-reloadable status. They should be discarded after use, and never mixed with Boxer primed cases. Since Berdan primers are little used and rarely encountered here in the U.S., all further references to primers will pertain to the Boxer type primer unless otherwise noted.

Primer Composition

One ingredient that proved to be a great source of trouble in early priming compounds was fulminate of mercury. Easy to manufacture and very sensitive, fulminate of mercury was the basis for most early percussion caps and primers. The real problems began when brass cartridge cases and smokeless propellants began to see widespread use. Upon firing, the mercury in the primer amalgamated with the brass, chemically attacking and weakening the case. As long as black powder was the primary propellant used in small arms ammunition, this effect was minimized by the milder primers then in use, and the lower operating pressures inherent to this type of propellant. When smokeless propellants became more prevalent, the damage caused by mercuric primers immediately began to create major difficulties. While the mercury caused no damage to the firearm itself, cases fired with this type of primer became brittle, rendering them useless for further reloading. The damage was caused instantly upon firing, could not be prevented, and could not be corrected afterwards. Mercury was soon identified as the culprit, and was promptly eliminated. Virtually all commercial primers have been made without fulminate of mercury since around the turn of the century, and are still clearly labeled as being “non-mercuric.” The U.S. military completely suspended the use of mercuric primers around 1898, so the likelihood of running into mercuric primers in anything other than extremely old, or some foreign ammunition is remote.

Corrosion was also a major problem in black powder firearms, due in part to the nature of the propellant itself, but largely to the qualities of the priming compound used in most early percussion caps and primers. Potassium chlorate, used as an oxidizer, was a primary ingredient in most of these mixes. Upon firing, some of this is deposited in the bore in the form of potassium chloride. Being very similar to ordinary table salt, potassium chloride is extremely hygroscopic, which is to say it attracts and holds moisture.

Naturally, this causes rusting in short order.

As potassium chloride is soluble in water, but not by most conventional bore solvents, its removal required very specific bore care techniques. Since most bore solvents were not effective in dissolving or removing this residue, some means of eliminating the potassium chlorate was needed. Oddly enough, it took many years and some exhaustive studies to determine what caused the gun corrosion problems experienced in this period. It was not until 1922 that Dr. Wilbert J. Huff, working for the Bureau of Mines at the request of the War Department, identified chlorate primers as being the source of this corrosion. Having located the agent causing the trouble, the next task was to eliminate it by finding a substitute. This proved to be a long and arduous task, despite the fact that rust-free primers were already in use with several foreign military services around the world. U.S. Ordnance was adamant concerning the reliability, storage life and stability of any new compound used in their priming mixtures. Their hesitancy to accept a new mixture was the result of a seemingly minor change on the eve of World War One, which nearly had catastrophic consequences. With U.S. troops already committed to combat in Europe, Frankford Arsenal was forced to literally shut down its primer production until the problem could be analyzed and corrected. After this experience, they approached new developments with an understandable degree of trepidation.

Eventually a priming compound was developed that omitted the potassium chlorate, using lead tri-nitro-resorcinate instead. Usually referred to as lead styphnate, this is still a common oxidizer in many of today’s primers. This mixture proved to give the stability and reliability demanded by the military, and was finally adopted after extensive testing. On the commercial front, many American manufacturers were already using noncorrosive primers in any of several different mixtures. Corrosive primers may still be encountered, even though their use was discontinued in U.S. commercial ammunition shortly after the First World War. Foreign military surplus ammunition containing corrosive primers (often of the Berdan type) is still frequently found at discount prices. Considering the problems that may be associated with its use, this ammunition may not be the bargain that it first appears to be. In U.S. military ammunition, chlorate primers were discontinued around 1950, but they may still be encountered in old lots of .45 ACP and .30-06 rounds. The .30 Carbine was the first U.S. martial cartridge that was loaded exclusively with noncorro-sive primers. Later U.S. surplus ammunition in either 7.62mm NATO or 5.56mm NATO poses no problem in this regard.

Today, small arms primers have evolved to the point of such extreme reliability that they are often taken for granted. This is a mistake, as primer selection and type can have a major effect on a given load’s accuracy and pressure. The components used in modern Boxer primers consist of 1) a cup 2) the pellet, or priming mixture 3) the foil, and 4) the anvil.


Despite their appearance, most primer cups are made of 70/30 cartridge brass. Most manufacturers apply a nickel plating to their primers for appearance sake, giving them their familiar silver coloration. The thickness of the various types has a direct correlation on the strength and sensitivity, largely determining whether it is suitable for a rifle or pistol. The more thinly cupped pistol primer may not hold the pressure of a high intensity rifle load, and may be pierced or blown if used in this type of application. The thicker cups common to rifle primers, on the other hand, may give misfires or accuracy problems if they are used in some pistols. Despite the dimensional similarities between the two types, they should not be interchanged. There are some handgun cartridges that have been designed to use rifle primers, such as the .221 Fireball, the 7mm TCU, and the .357 Remington Maximum. These, of course, should be used with the primers for which they were originally intended. When using the reloading data, please refer to the Test Components section for information on which primer was used for our load development.


The pellet is actual priming compound that is placed into the cup. As we have seen, all modern primers are both noncorrosive, and non-mercuric. Different amounts, and in some cases different types of priming compound may be used, depending on primer make, size and type.


Made of shellacked paper despite its name, the foil is a small circular disc placed between the priming pellet and the anvil. This acts as a shield for the pellet, protecting it from moisture and other disruptive influences that may effect performance or reliability. Some manufacturers color code this disc to aid in identification. However, since there is no standard coding among manufacturers, we recommend discarding any loose primers whose brand and or type has become suspect.


The anvil in a boxer primer provides the hard point against which the priming compound is crushed to detonate the primer. Like the cup, these are generally made of 70/30-cartridge brass rolled into thin sheets and punched into final shape. Most U.S. primers are of either two or three-legged design, with the three legged design being by far the most common. In examining a primer, you will note that the anvil extends a few thousandths of an inch above the cup. This is to allow the anvil to slightly compress the pellet when the primer is seated, thus sensitizing the primer. These statements hold true for both large and small sizes and for both rifle and pistol types.


The two predominate sizes of primers in use today fall into the basic categories of “small” and “large.” These may be further defined as being either rifle or pistol primers. Differences between the two include priming composition mixture, cup thickness and sensitivity, and very slight dimensional discrepancies in height. Within these sub-categories, the primers are defined still further, as standard, magnum, and in rifles, benchrest primers. Distinctions between these types vary from brand to brand, but most relate to composition mixtures, intensity and quality control standards during production. Diameters of the two sizes are .175″ for the small rifle and pistol, and .210″ for the large rifle and pistol, respectively. With so many different sizes and types available, how does the reloader know which type is appropriate for a given application? The following paragraphs will serve as a general guide for primer selection. In addition, the specific size, brand and type of primer used in our data development is listed under the Test Components heading for each cartridge in this manual.


Used with most of the smaller handgun cartridges, from the .357 Magnum down to the .25 ACP, when faster burning, easy to ignite powders are being loaded. Small pistol primers, either standard or magnum, must not be used for rifle cartridges. The higher operating pressures common to these cartridges (even when used in a pistol, such as the T/C Contender) presents a serious risk of pierced or blown primers if the thin-cupped small pistol primers are substituted for the correct rifle primer.

Examples: Winchester WSP, Federal No.100

Small Pistol Magnum

Small Pistol Magnum primers are an appropriate choice for cartridges such as the .357 Magnum when slow burning propellants are being used, especially ball or spherical powders such as H110 or Winchester 296. They may also be a good choice for non-magnum cartridges when extremely cold shooting conditions are encountered.

Examples: CCI 550, Winchester WSPM

Small Rifle

Although they share the Small Pistol primer’s diameter (.175″), the Small Rifle primers must not be randomly interchanged for pistol loading. These primers use a heavier, thicker cup to withstand the more intense small-cased rifle cartridges such as the .222 and .223 Remingtons. Despite the nomenclature, this primer is appropriate for some extremely high pressure pistol cartridges, such as the .221 Fireball and the .357 Maximum. They are also appropriate for loading rifle cartridges such as the .223 Remington when using handguns such as the XP-100 or T/C Contender.

Examples: Remington 6 1/2, CCI 400

Small Rifle Magnum

Providing a hotter or more intense flame than a standard primer, the Small Rifle Magnum is recommended for use with some ball powders, and those loads that will be used in subzero temperatures. They may also prove to be beneficial when very large amounts of powder are being ignited, as in wildcats such as the .22 Cheetah.

Examples: CCI 450, Federal 205

Small Rifle Benchrest/Match

Made with rigorous quality control standards, Small Rifle Benchrest/Match primers may provide somewhat better accuracy than the standard Small Rifle or Small Rifle Magnum primers. While this is not always the case, it is usually worth experimenting with these primers if the ultimate in accuracy is required.

Examples: Remington 7 1/2, Federal 205M


Intended for larger cases, such as the .45 ACP, .45 Colt, and 10mm Auto, the large pistol primer shares the same thin-cupped design as its smaller cousins. As such, large pistol primers present the same risks as the small pistol primers if they are indiscriminately used in rifle loads. Their use in rifles must be limited to those pistol cartridges that have been chambered in rifle designs, such as the .45 Colt in the Winchester M94 Trapper.

Examples: CCI 300, Federal No.150

Large Pistol Magnum

Large Pistol Magnum primers offer the added power sometimes needed for very large charges of slow burning pistol powders such as H110 and Winchester 296. With their greater power, they may also be a good choice for loads that will be used in subzero climates.

Examples: Federal 155, CCI 350

Large Rifle

Standard Large Rifle primers are the correct choice for most rifle reloading chores calling for the large primer. Adequate for all but the largest and most difficult to ignite charges, standard Large Rifle primers are probably the best choice for the vast majority of rifle reloading applications. We suggest opting for the magnum primers only after careful consideration of the type of cartridge being loaded, and the circumstances under which the ammunition will be used. Remember, the “Magnum” designation of a case does not necessarily mean that it will require or even benefit from a magnum primer.

Examples: Federal 210, Remington 9 1/2

Large Rifle Magnum

Large Rifle Magnum primers are made specifically for the larger charges of very slow burning powders common to the bigger magnum rifle cartridges. It is perhaps worth mentioning that some of this class of primers have been developed for very specific applications. The Federal 215 primer, for example, was designed to reliably ignite the massive powder charges associated with the Weatherby line of magnum cartridges. These should be used as shown in the loading tables, and must not be randomly substituted for standard large rifle primers. With their sharper ignition characteristics, they will frequently give higher pressures than a standard primer used in an otherwise identical load. As is true with the “Standard” large rifle primers, the “Magnum” designation does not necessarily preclude the use of these primers in non-magnum cartridges, but the load must be worked up again when primers are substituted.

Examples: Federal 215, Remington 9 1/2 M

Large Rifle Benchrest/Match

Large Rifle Benchrest/Match primers, like the small rifle variety, may offer improved accuracy in some load combinations. With the prospect of improved accuracy, match-grade primers deserve some consideration not only for competitive ammunition, but also for those hunting applications that demand extreme accuracy.

Examples: Federal 210M, CCI BR-2