Why primers fail

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 , 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. Weeks' data indicates That means you might hit a misfire every , 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 ,, 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.

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. The most common general cause of misfires is what's termed "insufficient indent.

You say, "Look at the indent. It was huge. I even hit it several times, and it still didn't go. 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.

Most people amplify beyond the linear part of the reaction, meaning inefficient primers will produce as much product as efficient ones. For sequencing, this is NOT the case. Inefficient primers will give only weak bands. It will not sequence, however. PCR reactions can be tailored to the primer; sequencing reactions cannot.

Unfortunately, we simply cannot do that in a Sequencing Core. I assume that primers are made by pouring a liquid primer mix into the cup after which it solidifies, maybe by cooling. Or there is another reason? Is there a pictorial primer pun intended of how the process works? When dried, it will perform as designed. Why primers fail is largely due to poor storage conditions.

Perhaps someone can explain the science behind this. Some of this ammunition came in to the US as surplus from Yugoslavia? One other rare source of primer failure is Bad seating Practice cracked pellet, but that is usually a problem for Over enthusiastic reloaders. Primers in ammo properly stored, in sealed containers, can survive for over years…I have fired 8mm Kropatschek Black Powder blanks, made in the early s, and they still light up quite well…admittedly the primers are Berdan.

Also, we have previously reported that mismatches in a heteroduplex oligonucleotide were captured by IMAC, and that single-stranded oligonucleotides were readily separated from double-stranded DNA [6]. However, the base content of an oligonucleotide is known to have a strong influence on its ability to bind to metal-chelate adsorbents.

The purines, adenine and guanine, have a strong affinity for the Ni-IDA matrix, while the pyrimidines, cytosine and thymine, have a much weaker affinity [6]. These results can be understood by reference to X-ray crystallographic studies [15] of nucleotide-metal ion binding sites Figure 1. Adenine, with its two metal binding sites, should show the best affinity, whereas thymine, with no strong metal binding sites, should show little or no affinity.

While guanine and cytosine each have one binding site, the guanine site is less sterically-hindered than that of cytosine. Consistent with these structural results, it was found that guanine has greater affinity for an immobilized metal than cytosine [6]. Thus, it can be expected that an oligonucleotide e. The pooled flow-through product from two identical columns was loaded onto a 1.

Figure 2A , lane 2 shows the purified PCR product; no primer band is visible in the product, indicating that both forward and reverse primers have been removed.

Figure 2B , lane 2 also illustrates the removal of the higher-mobility error products from the product mixture. Each wash was collected and analyzed on the same gel Figure 2A , lanes 3—5 showing that additional fractions of pure double-stranded product can be obtained if desired. The primer is eluted from the column in the first two elutions, along with more double-stranded product Figure 2A , lanes 6—9.

In Figure 2A , lanes 7—9 were concentrated fold by ethanol precipitation to enhance sensitivity. Lanes 7—9 were concentrated fold by ethanol precipitation to enhance sensitivity.

B Expanded views of bp product from selected lanes of Figure 2A. Error fragments are commonly produced in Taq PCR by insertion of mismatched bases [16]. The flow-through was collected from each column and analyzed on a UV spectrophotometer.

In the sequencing reaction, primers and nucleotides will compete with the sequencing primer and ddNTPs. Phred quality scores also can be used to assess the quality of the sequence, with a Phred quality score of 20 implying a 1-in probability that the base is incorrectly assigned [19] , [20].

Four independent PCR reaction samples were sequenced after each treatment, for a total of Each product was sequenced from each end using primers designated CT and NT , for a total of 24 reactions. Also, Phred quality scores for each base were provided by SeqWright. Figure 3 , showing a plot of the average Phred score versus base position obtained using the NT primer and a plot of the results using the CT primer shown in Figure S5 , demonstrates that the sequence quality is greatly improved for IMAC purified samples compared to that of unpurified samples, and is at least comparable to the quality observed for QIAquick purified samples.

For other experiments, an 1. The tube was centrifuged in a tabletop microcentrifuge at 11, xg for 2 min, the supernatant was decanted, and the beads were washed three times with DI H 2 O to remove residual ethanol. Then, 0.