Thursday, July 14, 2005

Primers, The Spark Plug Of The Cartridge.

The centerfire rifle and handgun primers are intricate and interesting little beasts. There are five different types available, Small Pistol, Large Pistol, Small Rifle, large rifle and .50 Browning Machine Gun. In the first four are also standard and magnum. The only difference between standard and magnum primers is that the flame from the magnum primer can be somewhat hotter and lasts a couple of gazillionths of a second longer. This helps in the ignition of large charges of powder, especially the ball powders which are coated with chemicals to retard burning. I know, coating the powder with something to keep it from burning seems counterintuitive but that's how they control the burning rates.

Large rifle and pistol primers measure .210 inch across, while small rifle and pistol primers measure .175.

An interesting historical fact is that two different people on opposite sides of the Atlantic Ocean invented the metallic centerfire primer at about the same time. The American,Hiram Berdan, invented a primer that require the anvil (more on what the anvil is and does in a minute) to be part of the cartridge case, eliminating the possibility of one central flash hole.

At the same about time a British Ordnance Officer, Edward Boxer, invented a primer that had an integral anvil. This made primer manufacture a little more complicated but simplified cartridge case manufacture. It also made handloading quite a bit easier,

In an interesting twist, the Berdan Primer, invented in America, is used in Europe and Britain while the Boxer Primer, invented in Britain, is used in the USA. This is primarily because the reloading of cartridges was very rare in Europe while very common in the US. Berdan primed cases are a major pain to try to reload. There are only two ways to decap a Berdan primed case, there is a decapping tool that like an old fashioned can opener, punches a hole in the primer and the handloader prys the cap out by using that hole. This, um, sort of works. Then there's the hydraulic method. Fill the case with water, put a tight-fitting rod in and rap it with a hammer. Water squirts everywhere and, after enough tries, the primer is pushed out. Do not try this outside in Wisconsin in the dead of winter. With it's central flash hole the Boxer primed case is easy to decap, a decapping pin in the sizing die pops it right out. Back in the day, a lot of foreign cartridges were only available in Berdan priming. Those cartridges were also expensive and hard to find. I've reloaded some of those, I hope to never do so again. Thanks to the size of the American market, even European companies like Norma, Sellior and Benoit and Lapua have shifted to Boxer priming.

If it weren't for handloading the Berdan priming system would be superior. The small size of the individual parts of a primer means that the fewer parts, the better. The two, or even three, flash holes in a Berdan primed case can make for more consistent and reliable ignition. It's not worth the hassle to the handloader, though.

The Boxer Primer is built from several different parts. First is the cup, that's the outside of the primer, a stamping of thin, fairly soft metal, usually brass, that contains everything else. Next is a very small amount of explosive. This explosive has changed over the generations. The first used was Mercury Fulminate. This was very effective with Black Powder. When smokeless came along the shooters of the day discovered discovered a major problem, the mercury attacked the brass of the cartridge case. Black powder left so much residue behind that it diluted that mercury so much that it was harmless.

The ammomakers searched for a replacement and found Potassium Chorate. The drawback to the Potassium Chlorate is that it leaves Potassium Chloride, chemically very much like salt, behind. This salt is hygroscopic, meaning it attracts moisture. This causes rust. In the old days this didn't matter, shooters were used to black powder the residue of that is just as prone to cause rust. As the memory of black powder faded shooters stopped cleaning their shootin' irons with soap and water. The solvents and oils used did nothing to wash that salt out of the barrel and shooters wondered why their barrels rusted. Meanwhile, military shooters knew to use water and their bores remained in good shape. American military ammunition continued using these primers up into the 1950s as they had to be concerned with long storage. As a youngster I shot a lot of surplus ammunition with such priming. My WW2 veteran mentors taught me exactly how to prevent rust along with stories of what did when water was short. In my youthful imagination I envisioned some eight million soldiers all peeing down their barrels in formation.

Eventually we settled on Lead Styphnate as the explosive. All American commercial ammo has been loaded with this priming since the 1940s, military ammo was phased in as the ordnance types became comfortable with these primers ability to work after decades of storage. This explosive, and the fuels that extend the flame, are all non corrosive now, nor do they attack the brass in the cartridge case. However, some foreign ammunition, especially military surplus, is still corrosive. If there is any question at all, err on the side of caution. Water is cheap. Just run a half-dozen or so sopping wet patches through, a couple of dry patches and then clean normally. Save peeing down the barrel for real emergencies.

In addition to the explosive Lead Styphnate, there is fuel and oxidyzer involved. Then there is a thin piece of foil put in. Then a little three legged anvil is put in and the whole affair is covered in shellac to waterproof it. In my youth these coatings were somewhat iffy. Handling primers with the slightest bit of oil on the fingers would kill them. In the last few decades the primer manufacturers have made great strides in oilproofing them. A couple of years back, in response to an argument on a shooting bulletin board I used to frequent, I conducted an experiment. I took a batch of primed cartridge cases and poured various things into them, enough to soak through the flash holes. I then left those cases for a week, and put them in my revolver and popped them off. I used WD-40, Remington Gun Oil, Three In One Oil and Kroil, a penetrating oil. Every one popped. This is by no means a definitive test, I only used one size and two brands of primers, Federal and Winchester Small Pistol. It is an indicator of just how far the technology has come since I was a boy. Naturally these advances came along after I got priming tools that eliminated the need for ever handling individual primers by hand. Even so, I like those tools, they're faster and more precise.

The difference between rifle and pistol primers is chiefly the amount of priming compound and the hardness of the cup. The rifle primer cups are thicker and stronger than in pistol primers, primarily because of the higher pressures involved. There are very few applications where one can safely use pistol primers in rifle cartridges and vice versa. About the only one that is widely accepted is in a cartridge like the .22 Hornet. Some specialty cartridges, the .454 Casull Magnum for instance, is made for the small rifle primer. I think I remember reading that the .500 S&W is also a small rifle but don't bet the farm on that.

When messing with primers one should bear in mind that a primer is the only part of a smokeless powder cartridge that is explosive and the only thing that is designed to pop by an impact. The packaging of primers is specifically designed to protect from such impacts. Primers should be kept in the original packaging until used. I'm aware of one case where a feller decided that he wanted to keep his primers protected from moisture so he dumped several thousand in a mason jar. He got away with it for quite some time. Eventually, though, it caught up with him and a bunch of them exploded while he was pouring some out of the jar. Didn't kill him but between broken glass and pieces of primers, well, he just wasn't very good looking anymore. Avoid jackass stunts, too. I know of a kid who wanted to hear some bangs so he set some primers on a concrete floor and whacked them with a hammer. They popped all right and the little anvil of one primer went into his cheek, just below the eye. Went right down to the bone, too. An inch higher and he would've been wearing an eyepatch. There used to be black dust that was escaped priming compound found in the tubes or trays of the various priming tools and, if we let it build up, became a danger. I haven't seen that dust lately, probably the same advances in water and oil proofing keeps the priming compound where it belongs. Still, if you see dust building up on your priming tools, clean it off with a damp towel or something.

Changing primers in a load can have an effect on pressure, velocity and accuracy. Usually we see minor pressure and velocity changes and they aren't always predictable. I have a pal who did extensive pressure and velocity testing on the .30-06 cartridge, testing dozens of loads with the same cartridge case, bullet and powder charge, changing only the primer. He saw no changes in pressure that would render a load unsafe unless that load was already at the red line. I keep my loads away from there anyway. If we are shooting a max load and want to try a different primer, back off and work up to max again. I don't have pressure testing gear, I have to work off visual signs and measurements of the fired cases so I do one last step to see if a load is safe. I load a very small batch and shoot it, reload the case and shoot it again. I repeat this until the primer pocket gets loose. If I can't get AT LEAST a half dozen loads out of a case, that load is too hot for long term use. I'd rather have more, like ten.

Well, that's about all I know about primers worth telling and probably far more than most people want to know. Next week we can begin exploring how to put all these parts together.

Update...after posting this I realized that I never explained what the anvil is. It's a little piece of metal shaped like the DANGER! RADIATION sign, that sits at the very top of the primer. The lead styphnate explosive, along with the fuel and oxidyzer is crushed between the cup and the anvil when the firing pin hits. A close look at a Boxer primer under a lottle magnification shows us that the 'feet' of the anvil stick out just a tiny bit past the cup. When we prime a case it gives the anvil a good solid base to resist the blow from the firing pin. That also serves to pre-stress the priming pellet, the mix of explosive, fuel and oxidyzer, increasing the sensitivity.

I also failled to mention the new lead-free primers for use in indoor ranges. These are, at present, only available in certain types of factory ammunition. The people who make them say that they won't be available to ordinary handloaders for the forseeable future as they require loading techniques that aren't available to us. Some indoor ranges do not allow lead bullets because they aren't well enough ventilated to keep the lead exposure to the range personel at a safe level. Since many of these ranges are police training ranges, owned by governments, instead of fixing the ventilation systems, they decided to blame the ammo makers. Typical. Since the lead-free ammunition is quite a bit more expensive than standard lead bullet reloads, it would be cheaper to simply install some decent ventilation systems. I remember the days when police practice ammo was reloaded, the work being done by trustees in the jails. Since petty criminals are rarely magna cum laude types this might remove some of the aura of difficulty and danger surrounding handloading.

1 comment:

jack fuller said...

This is what i am looking for. The most useful blog post that will expand my knowledge.
Pistol primers are indeed crucial aspects for consideration in case you have grabbed yourself a pistol. These particular primers are equally important like that of the rifle primers as well as magnum primers.