Making Accurate Bullets
January 04, 2011
Just about every shooter is on an everlasting quest for the utmost in accuracy. Here's how bullet makers help us achieve that goal.
What does it take to make an accurate bullet? Precision manufacturing!
We shooters are all alike in some ways. It really doesn't matter what type of firearm we prefer--the latest tactical semiauto, a super long-range varmint rifle, or a big-game gun. We have different opinions as to the best stock, barrel, caliber, or sights; but we're all on the same page when it comes to one issue: We all want accuracy. If our favorite firearm can't hit where we're aiming, it's pretty darn worthless.
A lot of factors go into making an accurate firearm. You must have a good barrel; you need a properly tuned action; a good trigger is a must, as is good sighting equipment; and you need to have all these components put together properly.
That about covers it, right?
Well, not quite. What about the ammo? Sure, for the best accuracy, we all know we need first-class ammo. This often takes the form of custom-made handloads that are worked up specifically for a specific gun. I'm willing to bet most of us have spent many hours at the reloading bench and out on the range working up loads. We try lots of different combinations of powders, primers, and bullets in our quest to find that "special load" that delivers the best possible accuracy.
More often than not, we decide on a particular bullet weight and type, and then we work from there. And generally, we hit the jackpot sooner or latter. Over the years, I've come to the conclusion that one of the reasons we so often do find that accurate load is because of the high quality of the bullets we now have available for use.
Years ago, I had several conversations about ammunition with a good friend who was a high-master shooter with several decades of experience. His advice was pretty simple: Always put a good barrel on your rifle, and always use a premium-quality bullet.
According to him, that would take care of most accuracy issues and give you everything you needed to win matches. And he should know, he's won lots of 'em.
While I no longer compete with a service rifle, in the last few years I've become hooked on prairie dogs. As you know, a prairie dog can present a pretty small target, and extended ranges of 200 yards or more are the rule. You need an accurate rifle, and you have to have good ammo...and lots of it!
As I've worked on my ammunition--and I'm doing that right now in preparation for my next prairie-dog shoot--I've done some thinking about bullets. I've been using Sierra bullets for years both for competitive shooting and for varmints. The accuracy has always been there. When I miss, I'm sure it's me not the rifle or the ammo.
Anyway, I started wondering about bullets and what it took to make really good ones. When you think about it, the stresses on a jacketed bullet are simply beyond incredible. Not only must the bullet withstand the explosive effect of the burning powder and being slammed into a rifled tube, it has to withstand the absolutely mind-blowing stress placed on it as it travels to the target.
A typical small-caliber varmint bullet traveling at an average velocity will have a rotational speed of as much as 500,000 revolutions per minute. The centrifugal force this creates literally tries to blow the bullet apart the instant it leaves the barrel. It makes you wonder how any bullet ever makes it to the target.
Gilding metal is furnished from the supplier in large rolls. After the cups are punched, the scrap gilding metal is just that, scrap. It can never be recycled to produce first-class bullets. Each cup undergoes progressive changes as it is processed through multiple stages. Individual bullet-jacket cups vary in size and thickness, depending upon its caliber and weight.
So, what makes a good bullet? What makes a premium bullet better than something you or I could put together at home? To answer that question, I took an afternoon trip over to Sedalia, Missouri, to visit the Sierra bullet company. Sierra is not the biggest bullet company in the country, but it definitely has a reputation for producing outstanding bullets used by competition shooters all over the world. I've used them for years, and when I was shooting NRA High Power, it was the standard. Lord knows how many little green boxes of Sierra bullets were sold each year at the National Matches at Camp Perry, Ohio.
At Sierra, the bullet-manufacturing process begins with a simple, flat sheet of gilding metal. Gilding metal is an alloy of 95 percent copper and 5 percent zinc used to form the bullet jacket. Not only do you need to use the proper alloy, you really should use virgin metal as well. Recycling may be appropriate in many places, but for premium bullets you must use a virgin alloy. According to the Sierra technicians, recycled gilding metal tends to be too brittle and just doesn't perform well. Performance is critical, as the use of a tough metal jacket enables the bullet to be fired at much higher velocities than a plain lead projectile. The jacket also provides greater control over bullet expansion and performance upon reaching the target.
The first step in the process of forming the jacket is to use a series of specially designed dies in a punch press to stamp out what looks like small cups from the flat sheet of gilding metal. These cups are then processed through multiple punch presses with a series of dies and punches until the cups are formed into thin, closed-end tubes. At this point, you can begin to see the resemblance to a bullet.
In order to get the optimal thickness of the jacket for a given caliber bullet and its intended use, they have to start with a specific sheet thickness of the gilding metal. One size doesn't fit all. As I recall, Sierra uses about 19 different thicknesses of gilding metal. Not only does this make production more efficient, it means there is less stress placed on the gilding metal as it's formed into the jacket.
In processing the gilding metal, it's necessary to anneal it in a controlled-temperature furnace. This keeps the gilding metal soft and pliable enough to allow it to be properly formed as it progresses through the various machines and manufacturing steps. Without annealing, the gilding metal would quickly work-harden and become far too hard and brittle. We see something similar to this as we reload our empty brass. The more often we resize it, the harder
it becomes, and the more likely case-neck cracks will form.
Of course, as the gilding metal is being repeatedly formed and shaped, it must be lubricated. Just as when we resize our fired cartridge cases, they have to use a lube, and it absolutely has to be one that's compatible with the material being formed as well as the machinery and dies. They also have to periodically wash, clean, and rinse the bullet jackets between manufacturing steps. These are little things that can't be ignored in the process of making really good bullets.
This huge machine is designed to anneal the bullet jacket cup with great precision and total temperature control. Below, freshly annealed jacket cups are shown as they leave the heat-treating furnace.
At the same time, they have to inspect the jacket at every step along the way. One of the critical keys to producing a superior bullet is to constantly check the manufacturing process. Without these checks, there's absolutely no way they can maintain the consistency needed for a superior bullet. They have to constantly check the jacket for thickness, length, and concentricity. Any variation to stringent standards will lead to inaccuracy and larger groups on target.
While the jacket is being formed, the lead for the core is also being processed. You might think that all cores are alike. It's just lead after all, but that's way off base. Sierra uses four different lead alloys for bullet cores, depending upon the particular bullet and its application. A bullet intended for competitive target work would not use the same lead alloy as one designed for varmints or one for big-game hunting. Pistol bullets might require a totally different alloy as well.
Lead cores can be made of 6 percent antimony and 4 percent tin, 6 percent antimony and pure lead, 3 percent antimony and pure lead, or 1½ percent antimony and pure lead. While this doesn't necessarily affect accuracy, it sure as the devil plays a role in how the bullet performs on impact.
The lead used for the bullet core starts out as a billet or large block. The billets are placed in a powerful press that extrudes the lead in the form of wire. Then, the wire must be wound on spools and annealed to relieve the stresses from the extrusion process and to stabilize it.
It amazed me to learn that they needed to anneal lead. I had no idea this was a step in the process, but that little detail is necessary to make accurate bullets.
The lead wire is run through various machines that cut it to a specific length and begin to form it to shape. They don't just cram a hunk of lead wire into a jacket. The piece of lead must be carefully formed so that it fits the jacket as close to perfectly as possible.
I had wondered about how the jacket was secured to the lead core and whether or not some type of bonding material or glue was used. Sierra doesn't use anything because it has found that any additional material has an adverse effect on accuracy. Besides, if the jacket is properly designed, of the right materials, and concentric, core separation is seldom ever a problem.
The jacket is also trimmed to a very precise length. This is essential so that the nose of the bullet can be properly formed and shaped. If there's too much jacket material, the opening for the hollow point or for the exposed lead tip could be closed off. Getting just enough jacket material but not too much requires experience and darn good engineering.
The core and the jacket come together in a machine where the core is swaged into the partially shaped bullet jacket. Here again, it's vital to have just the right amount of lead in the core. Too much or too little lead will have a disastrous effect on bullet weight.
Every manufacturer has standards, and the bullet weight must fall within certain parameters. In the case of Sierra, the weight must be within plus or minus 0.3 grain. My friends, that's not much margin of error. It goes without saying that the tighter the tolerances are, the more uniform the bullets will be. The more uniform the bullets, the greater the degree of accuracy you can expect to achieve.
Before the lead core is placed in the bullet jacket, it will be swaged to a specific shape (top). For this boattail match bullet, the lead core is swaged to match the boattail before it is inserted (middle). The nose has been formed on this bullet, and a bit of lead was extruded. It will be cleaned up at the next step in the manufacturing process (bottom).
After the lead core is secured, the nose of the bullet is formed. This may entail a final trimming of the jacket before the nose is swaged to shape. This swaging is done with a series of precisely machined dies.
It's also at this time that a synthetic ballistic tip may be added if needed for that particular bullet. After that, the completed bullets are cleaned in huge tumblers. From that point on, a bare hand will not touch them to prevent tarnishing from fingerprints.
One of the things I noticed at Sierra was the constant checking of every aspect of production. It seemed that each machine operator was always pulling out a micrometer or check gauge to measure the bullet at every stage of the process. In addition, there were folks who were checking the machine operators and pulling random samples for more detailed and in-depth dimensional checks. Detailed records are kept of every lot of bullets. The folks there are able to track an individual box of bullets and tell you when it was made, what machines were used, and who worked on it. If there's a problem, the source can be quickly determined, and corrections can be made.
That's great, but to consistently produce an accurate bullet, the manufacturers have to do even more than that. They have to shoot their bullets under controlled conditions.
One of Sierra's most unique and fantastic assets is located under the building where the bullets are made. It's a state-of-the-art, 300-meter, underground shooting range where random lots of bullets are pulled daily from production to test for actual shooting performance through one of the scores of benchrest-quality rifles of known accuracy. If a sample from a specific lot fails to perform, that entire production lot is pulled from inventory before the first bullet is sold. A similar process is used to test pistol bullets on Sierra's 50-yard pistol range.
The Little Stuff
One other element that contributes directly to the production of accurate bullets is having a fully equipped and staffed machine shop on site. This allows for total contro
l of the thousands of dies used in bullet production. In one sense, a bullet can only be as good as the tooling used to make it. By having the tooling produced in-house, a manufacturer never has to worry about a misunderstanding between the bullet makers and the tool and die makers. They're in the same place and can work together to quickly resolve any issues.
Once the bullets are completed, they are then inspected, counted, and boxed. Then--and only then--they are ready for the consumer.
All in all, it seems like a pretty simple process, and in one sense it is. I remember years ago reading about legendary barrel maker Harry Pope. He was the number one barrel maker in the country during the last part of the 19th and first part of the 20th centuries. As far as most shooters were concerned, no one else even came close to producing as fine and as accurate a rifle barrel as Pope. As you can imagine, lots of folks wanted to know his "secret" for producing these top-of-the-heap barrels.
Pope was pretty open about it. There was no secret. All he did was be very careful and methodical. He was constantly checking his work. This made him slow as molasses on a cold day if you were waiting for one of his barrels. However, that patience and attention to detail was what separated his barrels from the rest.
This machine trims bullet jackets to a very precise, pre-set length.
These are dozens of the barreled actions used for testing the bullets at Sierra. Each one has its own logbook.
The same is true with bullets. Anyone with enough money can set up a bullet factory. The equipment is readily available, and the actual production process is not a big secret. The difference between producing good bullets and ones that are not so good is in the details--the little stuff--and the willingness to constantly check the product at every stage of production. That takes time, resources, and a unique mind-set and commitment to quality and precision.
As shooters, we're fortunate to have a number of companies, large and small, that provide us with the very best bullets in the world. The men and women who make them are willing to focus on the smallest detail of every single step in the production of those bullets.
So the next time you shoot a great group or make a fantastic shot in the field, don't take all the credit. A lot of our success is due to the work of highly skilled and dedicated men and women who know how to make an accurate bullet.
Sierra Bullet Company
The Sierra bullet company got its start in 1947 when three California shooters--Frank Snow, Jim Spivy, and Loren Harbor--got together to make what they couldn't buy: a good, quality bullet.
At first, the bullets they made were for their own use, but word soon got out, and they began to supply a couple of local gunshops. It wasn't long before that hobby became a full-time business. Within a short time, Martin Hull joined the young company to help with marketing and product development.
In 1969, a group called The Leisure Group bought Sierra from the founders, and a fellow named Bob Hayden, an avid hunter and engineer, came on board as the manager. Several years later in 1991, BHH Management took over. Through all of this, Bob Hayden has remained at the helm.
In 1990, Sierra moved from Santa Fe Springs, California, to Sedalia, Missouri. In Missouri, the firm found a larger, more modern facility as well as a state that's a lot more supportive of business and the firearms industry. While Sierra is not the largest bullet maker, it does have a well-earned reputation for producing outstanding jacketed bullets for competition shooting and hunting.--Reid Coffield