WHAT IS A SEALED PRIMER, AND WHAT DOES IT DO? The modern metallic cartridge is the current pinnacle of ballistics reliability. The integration of primer, powder, and bullet into one compact, easy-to-carry package revolutionized gun design and continues to evolve to this day. While today’s ammo is sold as one complete unit, the separate components used to make each round can fail individually. This can cause a failure of the round to fire. The primer at the bottom of each round is one of the key points of failure in ammunition. If any foreign matter (usually a liquid) seeps inside the cartridge via the primer pocket, the chances of the round failing to fire go up significantly. If the primer fails to ignite, then the gunpowder inside the cartridge will also fail to ignite, and you won’t get a “bang.” To guard against this, many ammunition manufacturers coat the primer with a thin layer of lacquer or similar waterproofing material. This is supposed to protect the primer compound and gunpowder inside the cartridge. It helps ensure maximum reliability. But is that sealant effective? Is it really needed? Water and moisture are definitely a threat out in the field. Oil and other petroleum products have an adverse effect on primer and powder alike. Is a sealed primer pocket an effective defense against these outside contaminants? We sought to find out. TESTING SEALED PRIMERS VERSUS UNSEALED PRIMERS Our test ammo. Both use the same bullet, but they are not the same ammunition. We developed a test to measure the effectiveness of sealing the primer pocket. We shot 400 rounds each of two different rifle loads from Black Hills Ammunition: the 62 grain 5.56mm, which has a sealed primer pocket, and the 62 grain .223, which is unsealed. We immersed the rounds’ primer pockets in different contaminants for various amounts of time and then shot the rounds to test the results. 200 rounds of each load were immersed in water. 100 rounds were immersed in lightweight motor oil. The remaining 100 rounds were left alone as a control. We used reloading trays to ensure we were only immersing the primers in the fluid. We didn’t want moisture/oil/water to sneak in where the bullet and casing meet. We’re testing primer sealant, after all. After 24 hours, we wiped off, dried, and shot 50 rounds of each caliber that had been immersed in water, 50 rounds of each caliber that had been immersed in oil, and 50 control rounds. We saved the remaining rounds to fire 30 days later. The remaining rounds we covered in oil were wiped off and dried after 24 hours, then shot 30 days later. 50 rounds of each caliber were allowed to remain with their primers immersed in water for 30 days and then shot. Finally, 50 rounds of each caliber spent 24 hours with their primers immersed in water and were then removed from the water and sealed in an airtight container for 30 days. This was designed to mimic the effects of storing ammo in a very damp and humid environment. All ammunition was shot from an 11.5 inch AR-pattern pistol fitted with a Primary Weapons Systems AR-15 upper and a Sig Sauer suppressor. We tested the speed of both the 5.56mm and .223 rounds with a chronograph during each phase of the testing. To recap, the first phase of testing procedure was: To guard against any leakage from the cartridge neck or else where, we’ll use reloading trays to soak just the primers in each liquid. Black Hills 62 Grain .223, Non-Sealed (50 Rounds Each) Primers immersed in water for 24 hours, then shot Primers immersed in motor oil for 24 hours, then shot Control group Black Hills 62 Grain 5.56mm, Sealed (50 Rounds Each) Primers immersed in water for 24 hours, then shot Primers immersed in motor oil for 24 hours, then shot Control group The second phase of the testing procedure was: Black Hills 62 Grain .223, Non-Sealed (50 Rounds Each) Primers immersed in water for 24 hours, then shot 30 days later Primers immersed in water for 30 days, then shot Primers immersed in motor oil for 24 hours, then shot 30 days later Primers immersed in water for 24 hours, sealed in an airtight container for 30 days, then shot Black Hills 62 Grain 5.56mm, Sealed (50 Rounds Each) Primers immersed in water for 24 hours, then shot 30 days later Primers immersed in water for 30 days, then shot Primers immersed in motor oil for 24 hours, then shot 30 days later Primers immersed in water for 24 hours, sealed in an airtight container for 30 days, then shot RESULTS: TEST PHASE ONE Black Hills 62 Grain .223, Non-Sealed Primers immersed in water for 24 hours, then shot: No anomalies. Average speed of 2637 fps Primers covered in motor oil for 24 hours, then shot: No anomalies. Average speed of 2632 fps Control group: No anomalies. Average speed of 2623 fps Black Hills 62 Grain 5.56mm, Sealed Primers immersed in water for 24 hours, then shot: No anomalies. Average speed of 2832 fps Primers covered in motor oil for 24 hours, then shot: No anomalies. Average speed of 2876 fps Control group: No anomalies. Average speed of 2883 fps As you can see, performance was not negatively impacted after only 24 hours. To be honest, I’m not surprised by these results, as 24 hours isn’t very long for something to take hold inside the ammunition’s primer pocket. Let’s move on to phase two to see if more time yields a different result. RESULTS: TEST PHASE TWO Before we reveal the results of phase two, let’s pause for a moment to talk about what I was expecting to see here. I know from personal experience that when oil contaminates a cartridge’s primer, the primer is rendered pretty useless. Squib rounds are very common with contaminated primers, as are misfires and duds. Based on my experience, I was expecting to see some material impact on performance in the non-sealed .223 rounds after 30 days of contamination. I was also expecting the sealed primer pockets on the 5.56mm rounds to provide more protection from the effects of the oil and water left on the primer. That said, here are the results: The ammunition kept in a damp, watertight environment showed tarnishing on the brass and some smearing on the primer sealant. However, this did not affect reliability. Black Hills 62 Grain .223 Non-Sealed Primers immersed in water for 30 days, then shot: No anomalies. Average speed of 2606 fps Primers immersed in motor oil for 30 days, then shot: No anomalies. Average speed of 2610 fps Primers immersed in water for 24 hours, sealed in an airtight container for 30 days, then shot: No anomalies. Average speed of 2585 fps As a reminder, the control group for the .223 yielded no anomalies and an average speed of 2623 fps. Black Hills 62 Grain 5.56mm Sealed Primers immersed in water for 30 days, then shot: No anomalies. Average speed of 2779 fps Primers covered in motor oil 30 for days, then shot: No anomalies. Average speed of 22814 fps Primers immersed in water for 24 hours, sealed in an airtight container for 30 days, then shot: No anomalies. Average speed of 2822 fps The control group for the 5.56mm yielded no anomolies and an average speed of 2883 fps. WRAPPING UP THE SEALED VS. UNSEALED PRIMERS TEST Based on these results, it appears that cartridges with unsealed primers are as resistant as those with sealed primers to damage caused by water, oil, and humidity for periods up to 30 days. In addition, judging by the similarities in the chronograph results for each test, there does not appear to have been any powder contamination in any of the rounds we tested. Each round’s speed was comparable to that from the control group, indicating that the powder burned consistently, no matter what liquid it was soaking in. That does not mean there is no value in sealing your primers to protect your ammunition over longer periods. Our test only lasted 30 days. It is possible that a longer test could yield different results. It is also quite common for competitive shooters who reload their own ammunition to seal their primers to ensure maximum reliability. One dud round can make the difference between first and second place at a match. Sealing the primers on your match ammo gives you one less thing to worry about. ARE SEALED PRIMERS EFFECTIVE? Based on our test, we do not find that sealed primers improve reliability over unsealed primers over the short run. If your ammo is recently manufactured from a reputable manufacturer, then shoot it with confidence, regardless of whether it has a sealed primer. ABOUT THE AUTHOR Kevin Creighton Prior to joining the team at Ammoman.com, Kevin Creighton led the marketing for a number of companies in the firearms world. Kevin has been a gun writer since 2006, writing articles on the new reality of gun ownership in the U.S. for publications such as American Hunter, Shooting Illustrated, BearingArms.com, Beretta.com and also Downrange TV. He is an active competitor in USPSA, IDPA and 3 Gun and is an NRA-licensed firearms instructor. Kevin has hundreds of training hours from people such as Bob Vogel, Craig Douglas, Rob Leatham, Massad Ayoob and others.
I have some 405 grain 45-70 blackpowder that’s real old and it still goes bang. I also have some old 500 grain 45-70 smokeless that shoots ok. I would say both are close to 100yrs old. I don’t remember when I bought them but they were already old then. I have kept them in a army ammo can in the back of closet.
No old ammo here. I have some Mil stuff that is corrosive, so says the label on the Lead Wrapped and sealed outer cover, not that I plan on using it. I have a fair amount of Hand loads from a few years back, like 1980, which I sealed and use some every few years. No FTF yet. Temps storage would be factor but still no FTF. As a kid I got hold of some WW1 45 ACP Steel Cased US Gov rounds. I found the primers were very sensitive to minor contact. (Don't Ask) So loaded them up in a US Canteen, hit them with a 22 LR HP and had a massive hole in the Trinity River Clay Bank. Ahhh to be young and foolish again.
Interesting. I have some old 30-06 mil-surp ammo that someone gave me a few years back. Some of it is headstamped from 1936. I heard when I was a kid that mil-surp ammo loaded before about 1952 had corrosive priming. Thanks for the brain joggle, HK.
M1 carbine ammo was always noncorrosive. I think pre 1954 U.S. Mil surplus ammo was corrosive. Foreign ammo of any vintage should be looked on as corrosive.
Back when I was a cop I got a case of 1918 .30-06 (this would have been late 70's) and it fired just fine. It was corrosive and I had a few split necks but it shot well.
The only problem I've had with surplus ammo was with a case of 1950's FN .45acp ammo. A customer sold us a bunch of FN ammo .45acp and 30-06 along with a nice FN 49 rifle. I ended up buying the rifle and the pistol ammo to use in my Mac. They were in 25 round clear plastic packs and every one I tried was a dud. I tried about 75 of them and none of the primers would ignite. I ended up giving them away to a regular customer to pull the bullets.
