Introduction to primers
Cartridge primers, though small in size, plays a critical role in the functionality of ammunition. Its purpose, to ignite the propellant powder in a cartridge, propels the bullet, ultimately deciding the reliability of the ammunition. Therefore, understanding the primer—its sizes, types, and numeric ratings—is essential. This article aims to provide an in-depth look into the diverse world of cartridge primers.
The inception of the centerfire cartridge – the system that paved the way for modern ammunition as we know it today – was a pivotal moment in firearms history. The .22 BB Cap (Bulleted Breech Cap), also known as the 6mm Flobert, is widely recognized as the first rimfire cartridge, but it was the development of the .577/450 Martini-Henry that marked a significant step forward as the first centerfire cartridge to gain widespread acceptance.
The Emergence of the Centerfire System
The centerfire system was developed in response to the need for a more reliable, safer, and easier-to-manufacture cartridge compared to rimfire cartridges. The innovation of the centerfire system was that it moved the primer from the rim to the center of the cartridge base. This meant the cartridge could be thicker and stronger, which in turn allowed for higher pressures, resulting in greater velocity and energy.
.577/450 Martini-Henry: The Flagship of the Centerfire Cartridges
Developed by the British, the .577/450 Martini-Henry cartridge was first adopted by the British Army in 1871. It was designed for use in the Martini-Henry rifle, a breech-loading, single-shot, lever-actuated rifle. Named after Friedrich Martini, who improved upon the design of the Peabody rifle, and Alexander Henry, who designed the rifling, the Martini-Henry rifle was one of the most advanced firearms of its time.
The .577/450 Martini-Henry cartridge was a centerfire design with a Boxer primer. The original design had a paper-patched .45 caliber lead bullet pushed into a coiled brass case, with a bottle-neck shape that expanded to .577 caliber. It was filled with 85 grains of black powder. This design meant the cartridge could withstand the higher pressures needed for the approximately 1,350 feet per second (fps) muzzle velocity, a significant step up from previous cartridges.
Primer Development and the .45-70 Cartridge
While not the first centerfire cartridge, the .45-70 was the first centerfire cartridge to be adopted by the U.S military, thereby setting a precedent for future ammunition development in the United States. Adopted in 1873 for use in the Springfield Model 1873 rifle, the .45-70 was an early adopter of the Boxer priming system, named for its British inventor Colonel Edward M. Boxer.
This primer system, with its central flash hole and a replaceable, separate anvil, was a breakthrough because it was more reliable, safer, and easier to manufacture than the rimfire cartridges that preceded it. The centerfire design allowed the cartridge to be thicker and stronger, facilitating higher pressure loads, resulting in greater velocity and energy.
Impact on Future Ammunition
The .45-70's adoption of the Boxer primer was instrumental in setting the standard for future U.S. military and commercial ammunition. The straightforward design of the Boxer primer made it easily removable, thus making cartridges reloadable - a significant advantage that led to its widespread adoption in the United States.
While the .45-70 itself has been superseded in military use, its influence is still felt in ammunition design. The principles of its design, particularly the centerfire primer system, are found in nearly all modern ammunition. Furthermore, the .45-70 cartridge remains popular among hunters and shooting enthusiasts due to its power and effectiveness at short to medium ranges.
Anatomy of a Primer
Despite its small size, a primer is a complex piece of engineering composed of several different parts. Here's a breakdown of the key elements:
1. Primer Cup: This is the outer shell of the primer that houses all other components. It is usually made from brass or copper, which can withstand the firing pin's impact and the subsequent explosion inside the cup.
2. Anvil: This is a tiny piece of metal positioned within the primer cup. When the firing pin strikes the primer, the anvil provides the resistance necessary for the priming compound to be crushed and ignited.
3. Priming Compound: This is the chemical mixture that ignites when the primer is struck by the firing pin. The composition of the compound varies but typically includes lead styphnate, barium nitrate, antimony sulfide, and other chemicals. When ignited, it produces a flame hot enough to ignite the gunpowder within the cartridge.
4. Foil and Paper Disk: Some primers include a small disk made from foil or paper that separates the anvil and the priming compound. This keeps the priming compound in place during the assembly and handling of the primer.
5. Primer Pocket: While not part of the primer itself, the primer pocket is a key element in a firearm cartridge. It is the recess at the base of a cartridge case that holds the primer. It must be the correct size to accept the primer snugly. For reloading purposes, spent primers are removed from the pocket, which is then cleaned before a new primer is inserted.
Each of these components plays a crucial role in the function of the primer, and therefore, the entire cartridge. The precise design and assembly of these components ensure the reliable and safe function of firearm ammunition.
Primer Sizes
Primer size is an essential aspect to consider, as it must match the cartridge case. There are two key categories: small and large.
1. Small Primers:
Small primers typically measures about 0.175 inches (4.45mm) in diameter. They are commonly used in a variety of ammunition types, often those intended for smaller caliber firearms. Examples of cartridges that use small primers include .223 Remington, 9mm Luger, .357 Magnum, and .38 Special, among others.
Within the small primer category, there are subcategories based on specific use cases, such as:
- Small Pistol Primers: Used for standard pistol cartridges.
- Small Pistol Magnum Primers: Used for magnum pistol cartridges or standard cartridges with heavy loads.
- Small Rifle Primers: Used for rifle cartridges.
2. Large Primers:
Large primers have a larger diameter than small, typically measuring about 0.210 inches (5.33mm). They are used for larger caliber cartridges or those with higher pressure loads. Examples of cartridges that use large primers include .45 ACP, .308 Winchester, .30-06 Springfield, and many magnum calibers.
There are also subcategories for large primers:
- Large Pistol Primers: Used for standard large caliber pistol cartridges.
- Large Pistol Magnum Primers: Used for magnum large caliber pistol cartridges or standard cartridges with heavy loads.
- Large Rifle Primers: Used for larger rifle cartridges.
While this categorization covers most commercial ammunition, it's important to note that some special cases might require different primer sizes, such as the .50 BMG, which uses a unique, larger primer, and .17 Hornet, which uses a smaller primer.
Graf & Sons has a handy chart that is downloadable from their site that details sizes used in many types of ammo.
Primer Types
Primer type directly impacts the performance of the cartridge. Let's delve into four primary types:
- Boxer Primers: Boxer primers, mainly used in the U.S, are characterized by a central flash hole and anvil. They are popular due to their ease of removal and replacement, ideal for reloading.
- Berdan Primers: Often found in military and imported ammunition, Berdan primers feature two or more flash holes, with the anvil forming part of the primer pocket. These primers are generally more cost-effective, but the reloading process is more complex due to their unique design.
- Rimfire Primers: Unlike centerfire primers (Boxer and Berdan), rimfire primers form an integral part of the cartridge case. The primer ignites when the firing pin strikes the cartridge's rim, commonly used in small caliber rounds like the .22 Long Rifle.
- Shotshell Primers: Exclusive to shotgun ammunition, these come in two sizes, 209 (standard) and 209A (for magnum loads). The 209A variant delivers a hotter, more consistent ignition.
Primer Ratings
Primer ratings indicate the ignition power and the heat a primer generates—factors that can affect shooting consistency and precision.
- Standard Primers: Designed to reliably ignite a broad spectrum of propellants under normal conditions, standard primers are suitable for most shooting applications.
- Magnum Primers: These primers generate a longer-lasting, hotter flame, designed to ignite hard-to-burn propellants usually found in high-capacity rounds or those used in extreme cold. Using a magnum primer in place of a standard primer can lead to increased pressures and velocities, potentially creating unsafe shooting conditions.
- Benchrest or Match Primers: These are high-quality primers subjected to stringent quality control for maximum consistency. They are typically used in precision shooting, where minor variations in primer performance can significantly impact accuracy.
Primer Numeric Ratings
Specific primer brands, such as CCI, use numeric ratings (like CCI 300 or CCI 250) to classify their primers.
- CCI 300: This is CCI's designation for Large Pistol Primers, ideal for standard pistol rounds.
- CCI 250: Conversely, the CCI 250 represents Large Magnum Rifle Primers. As the label suggests, these primers are suited for magnum and heavy load cartridges.
Understanding the distinctions and functionalities of cartridge primers—their sizes, types, numeric ratings, and heat ratings—can drastically influence your shooting performance. Whether you're an enthusiast or professional, selecting the right primer is key for safety, reliability, and precision. Many reloading manuals cover primer information. When in doubt, find a good reference.
Here's a good place to shop for primers.
If you know of any forums or sites that should be referenced on this listing, please let us know here.
