Gregory Kielma • October 21, 2023
223 Remington/5.56 x 45mm NATO Cartridge
223 Remington/5.56 x 45mm NATO Cartridge
Hey Gregory,
Today's workbench is written by guest contributor and AGI Certified Gunsmith and GCA Moderator Robert Dunn:
There isn’t a day of my life that goes by that I don’t work with, reload, think or write about the .223 Remington and 5.56 NATO cartridges. Those cartridges are what a couple of my favorite and most used rifles are chambered for.
When I worked in an ammunition factory, I would sometimes get paid in .223 ammunition. When I was growing up in the early 1970s I became familiar with the .223 Remington cartridge, as it was the new round being used by our Armed Forces.
Warfighters throughout the world had realized the advantage of automatic firepower, but finding the perfect firearm and cartridge design is a huge challenge. In the case of the .223 Remington, many sources helped bring this cartridge into use by both civilians and the military.
Eugene Stoner of ArmaLite (then a division of Fairchild Industries) had gained the attention of the Military with his 7.62 x 51mm chambered AR-10 rifle. Like many high powered rifles, the AR-10 was hard to control during automatic fire.
Consequently, Fairchild Industries and Stoner were asked to scale down the AR-10 to fire a smaller caliber cartridge. Stoner came up with a prototype AR-15 and after a demonstration for the army, he was asked to produce more rifles for testing in 1957.
Select engineers and other companies like Remington Arms, Winchester as well as ArmaLite were asked to take part in developing this project. Springfield Armory’s Earle Harvey lengthened the .222 Remington case to the required specifications and it became the .224 Springfield, which was commercially known as the .222 Remington Magnum.
Frank Snow (of Sierra Bullets) and Eugene Stoner calculated the ballistics data for the .222 Remington to find the best bullet for the project, which ended up being a 55 grain bullet. Meanwhile, the Technical Editor for Gun and Ammo magazine, Robert Hutton, worked up a propellant recipe that could attain a velocity of 3,300 fps. Ultimately, Remington came up with the .222 Special cartridge, which was later renamed the .223 Remington because there were so many .222 designations.
Just a few of the military requirements for the firearm and cartridges were that they needed to be able to penetrate one side of a US Steel helmet at 500 yards, had to be able to exceed supersonic speed at 500 yards, had to be .22 caliber and select fire. From years of research and development of the AR-10 and AR-15, ArmaLite was facing financial difficulties and sold the rights for the rifles to Colt in 1959.
The AR-15 and the T44E4 rifle that would later be known as the M14 were being testing at the same time. To make a long story short, it was found that the AR-15 had far less failures per 1,000 rounds fired and that riflemen had a higher hit probability when firing Stoner’s rifle.
After Air Force General Curtis Le May test fired the AR-15, he ordered a batch of AR-15s to replace some of the M2 carbines that the Air Force was using. As the trials and testing continued, it was found that during marksmanship testing that many more men were achieving Expert shooting status with the AR-15 than they were with the M14. With these findings and the failure rate of the AR-15 going down even further, General Le May placed an order for 80,000 rifles in 1961.
In 1962, Remington filed the specs for the .223 Remington cartridge with SAAMI (Sporting Arms and Ammunition Manufacturer’s Institute) and the cartridge was later marketed commercially as a chambering for the Remington 760 rifle in 1963.
At this point in time, the United States was embroiled in the conflicts arising in Southeast Asia. It was politically decided that contracts for rifle manufacturing could be bid on by the private sector and Colt was awarded the contract to provide AR-15 rifles to fill orders for the Vietnam War.
The AR-15 rifle and the .223 Remington cartridge were formally adopted in 1964 and designated the XM16E1 rifle, commonly referred to as the M16, and the 5.56 Ball M193 cartridge. It was decided that the South Vietnamese troops would be supplied with the M16 rifle. Eventually, the Air Force, the US Army, Special Forces, the Coast Guard, the US Navy, the Marines as well as the SEAL teams had orders in for M16 rifles and cartridges. In 1965, Colt received orders for 800,000 M16E1 rifle and over 28,000 M16 rifles.
The M16 and the 5.56 Ball ammo would go through some major growing pains as the rifles and cartridges were issued to troops in Vietnam. Besides not being trained on how to properly clean the gun, the rifle suffered from many types of jams and failures.
Broken extractors and extractor springs accounted for many ejection failures and through more research, it was found that the propellant being used in the cartridges was creating horrific fouling of the gas and bolt system. The ball powder that was being used also created a longer pressure spike, which caused the case to expand in the chamber but it would not contract enough to be extracted.
The extractor would simply tear through the case rim, leaving the stuck case in the chamber. By using a different propellant, chrome plating the barrels and replacing the buffer with a new design that slowed down the cyclic rate, along with some other design changes, the problems were gradually sorted out. Unfortunately many American lives were lost because of these errors.
The process of selecting a smaller cartridge for use by NATO forces began in 1960. The cartridge design was based on the .223 Remington cartridge and its development was placed in the hands of FN Herstal. The rimless bottlenecked cartridge was named the 5.56 x 54mm NATO cartridge.
In 1980, the 5.56 NATO cartridge became the standard NATO rifle cartridge (known as the SS109 for NATO and the M855 for the United States). The 5.56mm cartridges allowed the soldier to be able to carry more ammunition, which equated to more firepower and logistically many more rounds could be transported to hot spots around the world by weight than the larger 7.62 NATO cartridges. On a global scale this can equal a savings of millions of dollars.
The number of firearms that are chambered for the 5.56 NATO cartridge is too numerous to list here. Just think about all of the different squad automatic weapons, rifles, carbines and machine guns that each NATO country uses…that is a lot of different weapons!
The Frankford Arsenal, Remington and Winchester produced the first lots of .223 ammunition for the United States Armed Forces. During the trials and testing of the AR-15, 19 Million .223 cartridges were purchased. When a cartridge does well for the military, the Law Enforcement and civilian communities usually follows their lead. If you have ever read the 27 page document for the military specifications for the M855 cartridge (5.56 x 54mm), you can see that heavy scrutiny has already been applied to the 5.56mm round!
The .223 Remington cartridge has become one of the most used cartridges in the United States. It is a great varmint and predator cartridge and could be used for larger game if need be by loading a heavier bullet like a Hornady GMX or Barnes TSX 70-grain projectiles. These slower moving heavier bullets seem to do quite well in windy conditions. The above attributes make the 5.56mm round a flexible survival cartridge too.
You may have noticed or even been annoyed by the interchanging .223/5.56 terminology, here are of the important similarities and difference between the two cartridges. The case dimensions are exactly the same, though case thickness/propellant capacity can vary significantly between manufacturers which will have an effect on the resulting pressures.
The 5.56 x 45mm NATO or other military 5.56 ammo tends to be loaded hotter, so chamber pressures will be greater than the typical .223 Remington load. For this reason, .223 Remington rounds can be safely fired in a 5.56 chambered gun but 5.56mm ammo should not be fired in a .223 Rem chambered gun.
The reason for this really comes down to the differences in the chamber dimensions between .223 and 5.56 barrels. The throat/free bore and leade of a 5.56mm chamber is longer. The throat of the chamber is the unrifled section of the chamber just forward of the neck and gives the bullet a place to sit. Leade or lead is the section of the bore of a rifled barrel located just ahead of the throat of the chamber. It is a conical shaped transition from end of the throat to the fully rifled part of the barrel.
In an effort to gain more accuracy from the 5.56mm NATO cartridge, Bill Wylde created the .223 Wylde, which is a chamber design that utilizes the same external dimensions and lead angle of a 5.56 NATO cartridge and the freebore diameter of the .223 Remington cartridge. Another company that uses a proprietary chamber design to achieve better accuracy from the 5.56mm NATO cartridge is Noveske. A Noveske barrel is not cheap but they are known for their precision and high quality products.
SAAMI specs are followed by manufacturers in the U.S. loading .223 Remington ammo but those same manufacturers who also load 5.56 ammo do not follow SAAMI specs because the 5.56 rounds are loaded to military specifications and thus not held to SAAMI specs. In Europe, the international organization C.I.P. tests and sets the safety standards for firearms and ammunition. In countries that are regulated by the C.I.P., .223 Remington ammunition is proof tested at the same maximum service pressure as the 5.56 x 54mm NATO cartridges.
There have been a lot of challenges that had to be met throughout the history of the AR-15 and the 5.56 x 54mm cartridge. The twist rate of a barrel and the chamber dimensions greatly effect performance and accuracy. The shorter barreled M4 carbines and the requests for even shorter barrel lengths coming from the Special Forces communities have kept firearms and ammunition engineers busy. At this point in time, the AR-15 style rifles and the .223 Rem and 5.56 NATO cartridges offer a very reliable and accurate shooting platform.
The AR-15 rifle and .223/5.56 cartridge combination have gone through many changes together. They are still being used by our Military/Law Enforcement and civilian populations to good affect every day. This combo is a must for 3-gun competition. The .223 Remington cartridge is not overly expensive and there is always a wide variety of ammunition to choose from. There is a lot of surplus ammo to select from as well. Many other firearms are chambered in .223 Rem besides the AR-15 type guns.
The 5.56mm round is a good cartridge to reload for, as there is a huge variety of quality components to choose from as well. In 1964, the year I was born, these cartridges were the new warfighting cartridge and the US Armed Forces began using them. It’s easy for me to remember how many years these cartridges have been in use!
Become an American Gunsmith and continue to preserve our Firearm’s Heritage!
Robert Dunn,
Gunsmith & Community Moderator
American Gunsmithing Institute
Gunsmithing Club of America
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Safety Starts With Everyone: It’s All About Awareness at Home or Work 01-16-2026 By Gregg Kielma Some gentle reminders that are the foundation of safety at home and work. Let’s Take a LOOK Safety depends on consistency, not complexity. Most accidents occur when warning signs are missed, so staying alert at home and work is key. Always be aware of your environment and keep these points in mind when planning for safety. A safe environment starts with simple habits: keeping walkways clear, maintaining working alarms, checking equipment regularly, and making sure everyone knows basic emergency procedures. Clear communication matters just as much. When people speak up about hazards or concerns, problems get solved early instead of after something goes wrong. Is your alarm system functioning at home? Have you checked that your fire extinguisher or extinguishers are up to date? Do you have fire blankets available? Is there a designated safe meeting place outside where your family can gather in case of a fire or home invasion? Responsibility ties it all together. Each of us plays a role in keeping our homes and workplaces safe. When you take ownership of your space and lead by example, others follow. As I always say, Stay Situationally Aware. Stay Prepared and ALWAYS, Stay Safe. Gregg Kielma
Why Owning a Firearm Is a Proactive Choice 01-16-26 ----By Gregg Kielma, Owner & Lead Instructor, Tactical K Training and Firearms My philosophy has always been and has never changed, being proactive means taking responsibility for your safety, your preparedness, and your peace of mind long before a crisis ever occurs. In my decades of training students across Florida and beyond, I’ve seen one truth stand out: owning a firearm—paired with proper training—is one of the most proactive steps a person can take to protect themselves and their loved ones. Let's Take a LOOK, My thoughts: Preparedness Begins Before the Emergency Most people lock their doors, install smoke detectors, and keep a fire extinguisher in the kitchen. Not because they expect danger every day, but because they understand that preparation saves lives. A responsibly owned firearm fits into that same mindset. It’s a tool you hope you never need, but one that can make all the difference when seconds matter and help is minutes away. Training Builds Confidence, Not Fear Proactive firearm ownership isn’t about paranoia or aggression. It’s about education, skill, and confidence. When you train regularly, you develop: • Safe handling habits • Clear decision making under stress • Respect for the responsibility that comes with carrying a firearm • The ability to protect yourself without hesitation or uncertainty Confidence is not built in the moment of crisis. It’s built on the range, in the classroom, and through consistent practice. A Mindset of Responsibility Owning a firearm proactively means embracing a higher standard of responsibility. That includes: • Secure storage • Understanding the law • Maintaining your equipment • Staying current with training and best practices This mindset doesn’t just make you safer — it makes your household and your community safer as well. Empowerment Through Knowledge Knowledge is power, and proactive firearm owners invest in learning. They understand situational awareness, conflict avoidance, and de-escalation. They know that the best fight is the one you never have to be in. A firearm is simply the final tool in a layered approach to personal protection. Kielma’s Parting Shot: Protecting What Matters Most At the end of the day, being proactive is about protecting the people you love. It’s about refusing to leave your safety entirely in the hands of others. A firearm, when paired with proper training and a responsible mindset, gives you the ability to act decisively when it matters most.
AED's For Home and Business Why? Let's Take a LOOK Gregg Kielma January 15, 2026 As someone who is certified to teach CPR and sells Defibrillators, I'm often asked if you should have an AED at home. The answer is yes—during a heart attack, every second counts. Using CPR with an AED can save the precious lives of family friends and loved ones. The cost of home defibrillators is minimal compared to the alternative. Most home AED’s cost $700.00-$1000.00 depending on make and models. Expensive? Not really when lives matter. Having an Automated External Defibrillator (AED) in both your home and business is one of the most powerful steps you can take to protect the people who matter most, family, friends, coworkers and customers. Sudden cardiac arrest can strike anyone, anywhere, and every minute without intervention dramatically reduces the chance of survival. Emergency responders do incredible work, but even in the best conditions, they may be minutes away and those minutes are critical. During a cardiac event every second counts. An AED bridges that gap by giving everyday people the ability to deliver life‑saving action before help arrives. Modern AEDs are simple, intuitive, and designed for anyone to use, even under stress. For families, having an AED at home means you’re prepared for the unexpected, especially if you have loved ones with heart conditions, active lifestyles, or higher risk factors. For businesses, an AED demonstrates a commitment to employee and customer safety, strengthens your emergency response plan, and can significantly reduce liability by showing you took reasonable steps to safeguard your environment. At Tactical K Training and Firearms, I believe preparedness is more than equipment, it’s a mindset. An AED is not just a device; it’s a life‑preserving tool that empowers you to act decisively when seconds matter. Thank you for reading if you like this article please let me know. Gregg Kielma, Tactical K Training and Firearms
Gregg Kielma The Smart Gun Owner: A Model of Responsibility and Preparedness By Gregg Kielma Tactical K Training and Firearms 01/14/2026 I regularly teach my philosophy, "Always Be Safe," focusing on safe and responsible firearm handling. A smart gun owner is more than someone who simply possesses a firearm. They embody a mindset—one built on responsibility, awareness, and a commitment to safety. In communities across America, smart gun owners play a vital role in promoting safe practices, protecting their families, and setting a positive example for others. Their approach to firearm ownership reflects maturity, discipline, and respect for the tools they carry. Knowledge First, Always: Smart gun owners understand that education is the foundation of safe firearm ownership. They seek out training, stay informed about current laws, and continuously refine their skills. Whether it’s mastering safe handling, improving marksmanship, or learning about situational awareness, they recognize that knowledge is their most valuable asset. Safety as a Way of Life: For the smart gun owner, safety isn’t a checklist, it’s a lifestyle. They store their firearms securely, handle them with care, and follow established safety rules every time. Their habits reduce risks, prevent accidents, and set a standard for others to follow. By modeling safe behavior, they help create a culture where responsibility is the norm. Protecting What Matters Most: Many people choose to own firearms for personal and home defense. Smart gun owners take this responsibility seriously. They understand that a firearm is a tool of last resort, used only when escape or avoidance is impossible. Their focus is on protecting loved ones, not seeking conflict. This mindset reinforces the true purpose of responsible ownership: preserving life. Commitment to Skill and Discipline: Smart gun owners know that proficiency doesn’t happen by accident. They practice regularly, maintain their equipment, and stay sharp. Their discipline extends beyond the range—into how they think, plan, and prepare. This dedication ensures they are capable, confident, and ready to act responsibly if the need ever arises. Leaders in Their Community: By sharing knowledge, encouraging safe practices, and supporting others, smart gun owners strengthen their communities. They help dispel myths, promote responsible behavior, and demonstrate that firearm ownership—when paired with education and respect—can be a positive force. Their leadership inspires others to follow the same path of responsibility. Kielma’s Parting Shot: A smart gun owner is defined not by what they carry, but by how they think and act. Their commitment to safety, education, and responsibility sets them apart. They are protectors, learners, and role models—individuals who understand that owning a firearm is both a right and a profound responsibility. Gregg Kielma
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Why Real Estate Agents Should Prioritize Safety Training Gregg Kielma 01/11/2026 Please stay safe Friends in the Real Estate Business. Here are my thoughts and what I teach. Kielma advises real estate agents spend their days meeting strangers, entering unfamiliar properties, and working alone in unpredictable environments. While the industry focuses heavily on sales skills and market knowledge, personal safety is just as essential. Safety training equips agents with the awareness, confidence, and practical tools they need to protect themselves while serving clients professionally. A High-Risk Profession • Agents often meet clients they’ve never met before, sometimes in vacant or remote locations. • Open houses and showings can attract anyone—including individuals with harmful intentions. • Many incidents involving assaults, robberies, and threats occur during routine real estate activities. Situational Awareness Saves Lives: These skills help agents avoid dangerous situations before they escalate. Safety training teaches agents how to: • Recognize suspicious behavior early • Maintain control of their environment during showings • Use safe positioning and exit strategies • Trust their instincts without feeling unprofessional Professionalism Includes Personal Protection Clients trust agents to guide them through major financial decisions. An agent who prioritizes safety demonstrates responsibility, preparedness, and professionalism. Safety trained agents are more confident, make better decisions under stress, and reduce liability for themselves and their brokerage. Empowerment Through Education: This knowledge benefits them not only in their career but in everyday life. Safety training empowers agents with: • De-escalation techniques • Communication strategies • Legal considerations for self defense • Practical tools for staying safe on the job Kielma’s Parting Shot Real estate agents face unique risks that can’t be ignored. Safety training isn’t optional, it’s a critical investment in personal well-being, professional credibility, and long-term career success. Brokerages that encourage or require safety training show they value their agents and are committed to creating a safer industry.
