The Truth About Primer Misfires
November 29, 2017
Let's say you were just out training and experienced a misfire. You replaced the round in the chamber and hit it again. The damned thing still didn't go off! The primer hit is deep, and to top it off, later in the day you have another misfire. Bad ammo, right? Maybe not.
Primers are constructed of three basic components: a cup, which is the part that is visible at the base of a cartridge case; an anvil, which is a small, tripod-shaped piece of metal; and an impact-sensitive explosive, normally lead styphnate. Just like the name suggests, the cup is shaped like a cup and contains the explosive primer mix sandwiched between the bottom of the cup and the anvil. Primers are designed to be struck in the center by the firing pin with a specified force in order to ignite the cartridge. When the primer is struck, the cup indents inward, causing a shearing action on the impact-sensitive explosive as the firing pin crushes it against the anvil in the primer, detonating the primer. Primers ignite with incredible reliability. In the words of notable Winchester ballistician Glen Weeks:
"Based on the SAAMI-specified drop test, statistics will tell you that our primers are 99.9997 percent reliable. That means that when struck with sufficient energy and properly centered, they will go off 99.9997 percent of the time. A lead-styphnate primer is probably one of the oldest and most reliable devices on the planet."
Misfires do happen, but misfires due to a defective primer are very rare. My company, Black Hills Ammunition, test fires more than 100,000 rounds per year, every year. It sells tens of millions of rounds each year to customers who are very demanding. When a misfire is encountered during testing, or if a misfire is reported by a customer, the company fully investigates the cause. These investigations over the years have shown that misfires were the result of a defective primer in only a very small percentage of the incidents.
The point is about statistics. Primers are not perfect — nothing man-made is — but they are very reliable. Statistically, you might encounter a defective primer, if you shoot enough. Mr. Weeks' data indicates 99.9997 percent reliability. That means you might hit a misfire every 300,000 rounds. Black Hills' experience does not indicate even that high of a misfire rate. The company visually inspects every one of the many millions of primers it gets yearly from Winchester and other primer manufacturers before they go to the loading operation. Over the years, the average is one rejected primer in about every 250,000, but most of the flaws are minor defects or damage such as slightly out-of-round primers that would have no effect on reliability. The company can't visually inspect the interior of primers that come to it in the form of primed brass such as the .308 brass, but it does inspect for proper insertion, appearance and depth.
In the scenario we started with, our hypothetical shooter had two misfires in one training session. The odds of encountering two misfires due to defective primers in one day are beyond remote. "So," you ask, "what can cause this type of misfire situation if it isn't defective primers in most of the cases?" There are a number of possibilities.
DENTS IN PRIMERS
The most common general cause of misfires is what's termed "insufficient indent." That means the primer was not struck with sufficient force. You say, "Look at the indent. It was huge. I even hit it several times, and it still didn't go." Primers are set up with a very precise orientation of primer component parts. If the primer is hit once and it does not go off due to insufficient firing-pin force, the sensitivity is further decreased. The primer mix, called a pellet, may have been cracked and moved out of the way from between the cup and the anvil. The primer mix is intended to detonate when sheared between the cup and the anvil by the primer strike. If the first blow is insufficient, the second one is now trying to ignite a primer that was damaged by the first strike. Sometimes the primer will go with a follow-up hit, and sometimes it won't.
Hitting it again doesn't prove anything either way. It does, however, make the indent deeper so it looks to the average viewer that it certainly should have gone off. It also destroys the evidence necessary to do a good investigation. Therefore, if you have a misfire and want to investigate the cause, do not try firing the round again. Think of it as similar to a car accident investigation. Would it be good scene preservation to have the cars back up and hit each other again to help you analyze the physical evidence? If you want to know why a primer did not go off, save the misfired round along with the box it came in and contact the manufacturer for instructions on returning it for examination.
How can a firearm cause a misfire due to an insufficient indent? One possibility is a damaged firing pin, one that has either a bent or chipped tip. Another possibility is that the firing-pin spring is too weak. The spring may be dragging on the interior of the bolt body or impeded by grease in the bolt, especially under cold conditions. The pin may be dragging on an improperly aligned firing-pin aperture, or it may be too short. Misfires can even be caused by excessive headspace. Basically, headspace is the measurement from the slope of the shoulder to the base of the cartridge, or the corresponding dimensions in the rifle chamber. Excessive chamber headspace allows the cartridge to be farther forward in the chamber away from the firing pin, or it can allow for the cartridge case to move forward when struck by the firing pin. Certainly, this can affect ignition reliability and cause misfires.
IMPROPER LOADING TECHNIQUES
Improper loading techniques can cause perfectly good primers to perform poorly. For best sensitivity, the primer should be seated firmly to the bottom of the primer pocket, but not unduly crushed into place. The legs of the anvil are slightly compressed during the seating process, which can cock or tilt the primer. If the primer is not seated to the bottom of the primer pocket, it's not as sensitive, and the primer can also move forward slightly upon impact by the firing pin, cushioning the impact force. Conversely, if the primer is seated with too much force, it sits deep in the primer pocket, causing it to be farther from the normal position for firing-pin impact, and the primer anvil can be pushed through the primer mix to the bottom of the primer cup. If there is insufficient mix remaining between the cup and anvil, the result is a misfire.
If a cartridge case has insufficient headspace due to a manufacturing defect, misfires can result. If the case is undersize, it can move forward in the chamber upon firing-pin impact just as if the chamber were too long. Contamination of the primer by moisture or oil can also desensitize the primer, resulting in a misfire. These causes are not typically seen in factory-loaded ammunition due to quality-control procedures. They are more commonly seen with handloaded ammunition.
Another common cause for misfires from a perfectly functioning rifle and good ammunition is failure of the operator to completely close the bolt before firing. If the bolt handle is lifted even slightly from the completely closed position, a misfire can result. I discussed this with George Gardner of GA Precision. He advises:
"It's very common for the user to get caught up in the moment of a match or training exercise and blow one of the easiest things to do — close the bolt completely. Speed is not always the best option, as smooth is faster. When the bolt is not fully closed, the firing-pin cocking piece drops onto the camming surface of the bolt and not in the open notch that is there for clearance. This robs a lot of the energy from the firing pin."
I suggest you try this demonstration the next time you go to the range. Unload your rifle. Double-check to make sure it is unloaded. Close the bolt, then raise the bolt very slightly. Squeeze the trigger while watching the bolt handle. You can see the bolt handle snap closed. The energy to make that happen is being robbed from the firing-pin velocity and energy normally used to strike the primer. Failure to completely close the bolt is easy to do, especially under speed drills, stress and position shooting. Normally, we get away with it. Sometimes it induces a misfire. I discussed this with Charlie Milazzo, firearms advisor to the American Sniper Association (ASA). He said, "Failure to completely close the bolt is probably the single most common cause of all misfires in sniper rifles."
DIFFERENCES IN BRANDS
As an ammunition manufacturer at Black Hills Ammunition, I have the obligation and opportunity to investigate misfires. One common situation is that the shooter reports, "I know it can't be anything wrong with my rifle because I've never had a misfire with brand XYZ." While all U.S. primers are made to an industry specification, the specification is a range, not a specific, absolute, identical performance standard. Some brands of primers are more sensitive than others. This isn't because of quality differences, it's by design.
Everything in life is a compromise. Primer manufacturers have to make choices. My company, Black Hills Ammunition, uses Winchester primers. I have discussed this topic at length with Winchester. The company could make its primers more sensitive, but that increases the possibility of a slam-fire. A slam-fire is the premature detonation of the round in the firearm from impact by the bolt or, in some cases, an inadequately restrained firing pin. This can happen most frequently during the feeding process and prior to the round being fully chambered in a semiautomatic or automatic firearm. Consequences of a slam-fire are generally more serious than a misfire from a light strike (60,000 psi of escaping gases from the breech area and next to your face is not a good thing). Military primers are made with an even thicker cup than the one used in commercial primers — specifically for this reason. Think about that. If a sniper rifle will work only with its favorite brand of commercial ammunition, what would happen if you fed it MIL-SPEC ammunition?
Winchester advises that it could also make primers more sensitive by using a different anvil configuration, but while this increases sensitivity to centered primer hits, it decreases sensitivity to slightly off-center hits. Winchester chose to stay with safe, reliable performance in a wide range of circumstances. Primer manufacturers and ammunition manufacturers have to load for everyone's rifle. Most snipers shoot bolt-action rifles. However, ammunition manufacturers have to make ammunition that is safe in every rifle out there. They can't make primers more sensitive and label them "Not for use in semiautomatic rifles." Do not confuse sensitivity with reliability. Primers are incredibly reliable when struck with industry-specified force.
So what does it mean when the rifle experiences no misfires with one brand of ammunition and primer but has misfires with other brands? My opinion (and that of Charlie Milazzo) is that such a rifle is marginal in performance. The sniper using such a rifle is betting against fate that the rifle will work when he needs it. I suggest he resolve the light-strike issue with the rifle, then use whatever brand of primer and ammunition he prefers.
DAMAGED BY CONDITIONS
Ammunition can become contaminated. The most common culprit is light penetrating oil. Oil is an extremely effective desensitizer of primers. That's the biggest reason why most ammunition has lacquer-sealed primers. Moisture can also damage primers, but moisture is not nearly as likely as light penetrating oil to actually penetrate into the primer. Brief exposure to moisture in the field is normally well tolerated by ammunition. Long-term exposure such as storage in damp conditions can destroy ammunition (and so can pressurized water exposure such as diving with your ammunition).
Misfires are not that uncommon. Misfires due to a defective primer, however, are rare. That means that if you have a misfire, you should thoroughly have it investigated to determine the cause so you can fix the problem. You don't want a misfire during a critical incident. Don't just chalk up the next one as a bad round and move on. Any sniper, team leader or commander who accepts misfires and does nothing to investigate and fix the problem is making a mistake that can have severe consequences. As professionals, when we identify a problem, we are obligated to determine the cause and take preventative action.
The most common cause of misfires in a bolt-action rifle is operator error. This is often masked, because the bolt closes completely upon pulling the trigger. The good news is that this problem can be corrected though awareness, training and diligence on the part of the operator. If you're confident that the misfire was not due to operator error, save the round and the box it came in, and contact the ammunition manufacturer so that it can investigate. A reputable manufacturer will cooperate fully with your request to have the ammunition examined to determine the cause of the misfire. Do not try to fire the round a second time, because that hampers the ability of the ammunition manufacturer to investigate the misfire. You should also have the rifle thoroughly checked by its manufacturer. When you call, be sure to let the manufacturer know that yours is a sniper's rifle. This should aid in getting a thorough and prompt response from the company.
As a sniper, you train hard to make sure you are capable of doing your job when called upon. It is not unreasonable to expect the same level of reliable performance from your rifle and ammunition.
Jeff Hoffman has been a law enforcement sniper since 1989. He is a reserve deputy in Pennington County, South Dakota, and a sniper team leader of the Pennington County/Rapid City SRT. He is president and co-owner of Black Hills Ammunition Inc.