Primers, the Sparkplug of Centerfire Cartridges
By Chuck Hawks
The primer ignites the main powder charge in the cartridge case. Without a good primer, nothing happens when a gun's firing pin falls. All ammunition commercially loaded in the U.S., as well as reloaded ammunition, uses the self-contained "Boxer" type primer, developed by Edward Boxer. This little device has a cup, which holds the priming compound, and an anvil. The anvil rests lightly on the priming pellet, which is crushed between the dent made by the impact of the firing pin and the anvil to initiate ignition.
European cartridges have traditionally used primers of the "Berdan" type, developed by Hiram Berdan, which lack the anvil of a Boxer primer. In a cartridge designed for a Berdan primer the anvil is built into the primer pocket of the case, rather than the primer. These cases can not be de-capped and reloaded by standard reloading tools. I understand that, as reloading catches on with European shooters, an increasing number of European cartridges are being factory loaded with Boxer primers.
It is a quirk of history that Edward Boxer was a British ordinance officer, yet his primer design was adopted in the U.S. Hiram Berdan was an American ordinance officer, yet his primer design was adopted in Europe, as well as most of the rest of the world.
The priming compound itself is an explosive intended to be detonated by percussion. (It can also be detonated by heat or flame.) There is typically less than one grain of priming compound in even the hottest primers. Never the less, primers must be handled and stored carefully. They are, after all, designed to start a fire. Store primers in the proverbial cool, dry place away from other flammables. High humidity degrades primers more than high temperature. According to CCI/Speer, properly stored primers will remain viable for decades.
Keep different types of primers separated so that they cannot be confused. Always store primers in their original packaging, which is designed for safety. Never store primers in bulk, such as in a can or jar. In many jurisdictions it is illegal to store more than 10,000 primers in a private home.
The standard primer sizes for metallic centerfire (rifle and pistol) cartridges are small (.175" diameter) and large (.210" diameter). The standard primer types are pistol, pistol magnum, rifle, and rifle magnum.
Rifle primers use tougher cups than pistol primers because the firing pin blow of rifles is usually harder than the firing pin blow of pistols. Rifle primers also contain more priming compound than pistol primers, since rifle cartridges typically contain more powder than pistol cartridges.
Magnum primers are "hotter" than standard primers. CCI/Speer typically recommends that magnum primers be used with ball (or spherical) powders, when loading magnum or other large capacity cases, and when it is anticipated that the cartridges will be used at temperatures below 20 degrees F. Ball powders are generally harder to ignite than flake and extruded powders and magnum primers are often called for, even in non-magnum rifle and pistol cartridges. Let your reloading manual be your guide to primer selection.
The common primer brands encountered in the U.S. are CCI, Federal, Remington, and Winchester. I have used all four of these brands, and they are all perfectly satisfactory. In addition, RWS (Boxer type) primers are sometimes available in North America, and are common in Europe.
Each of these brands has their own designation for the specific type and size of metallic centerfire primer. Here are the standard primers by brand. (There are also a few match, bench rest, and mil-spec primers, which are not included here.)
All U.S. made shotshell primers are designated #209, regardless of company of manufacture. #209 primers are used for all shotgun gauges. They are known as "battery-cup" type primers. This is a two-part primer design in which the anvil and primer cup are supported in an external cup. Shotshell primers are larger and shaped differently than metallic centerfire primers. This makes them immediately identifiable. The two types cannot be interchanged or confused.
Primers affect the pressure generated by the cartridge. Changing from standard to magnum primers may substantially raise the maximum average pressure of the cartridge and indiscriminate changes are not recommended. The A-Square Company conducted pressure tests involving six different primers. These tests used the 7mm Remington Magnum cartridge with a 160 grain Sierra BT bullet and 66.0 grains of H4831 powder and the results were reported in the A-Square reloading manual Any Shot You Want. A-Square used CCI 200 and 250, Federal 215, Remington 9 1/2M, and Winchester WLRM and WLR primers in these tests. They revealed a total spread in pressure of 12,800 psi from the mildest standard (the CCI 200) to the hottest magnum (WLRM) primer tested.
Changing brands but using the same type of primer will also usually result in pressure changes, but ordinarily these will be less drastic. In the A-Square tests the pressure spread between the CCI 200 and the hottest standard primer (the WLR) was 9600 psi. The spread between the mildest magnum primer (the Rem. 9 1/2M) and the hottest magnum primer (WLRM) was 8300 psi. These are significant pressure variations that cannot safely be disregarded.
Incidentally, these same tests revealed that the Federal 215 and CCI 250 large rifle magnum primers produced nearly identical pressures. The difference between these two primers was only 100 psi. A-Square also reported that, while they had not tested these two primers in all possible cartridges, this result was typical of their experience with these two primers.
Basically, I follow the recommendations of whatever reloading manual I am using as a reference regarding the proper brand and type of primer to use. For example, if the load in the manual was developed using a WLR large rifle primer, then that is what I use. If one brand of primer (of the same type) must be substituted for another, the conventional wisdom is to reduce the recommended powder charge by 10% (assuming the load is not already at the minimum) and work back up slowly.
I don't know how valid it is, but the opinion of many reloaders seems to be that Winchester primers are generally the "hottest," Federal and CCI are the middle brands, and Remington primers are the mildest. That is also my impression, but understand that it is based on rumor and supposition, not fact.
When reloading, always seat primers slightly below flush with the head of the cartridge case. This insures that the anvil is properly pressed against the priming compound for reliable ignition. Failure to properly seat primers is the biggest single cause of misfires in reloaded ammunition. A good depth to aim for is .005" below flush. With some experience this can be determined by feeling the case head after the primer is seated. Any primer that is flush or protruding should be very carefully removed and the case reprimed. Decapping a live primer can set the thing off, so behave accordingly and take all necessary precautions, including ear and eye protection.
For hunting and general recreational shooting purposes I have not ordinarily seen a significant difference in accuracy attributable to using different brands of primers. However, there are exceptions to this general observation. Some loads do seem to work better with a certain primer. Sometimes the chronographed standard deviation in the velocity of a load is lower with one brand of primer than with another. In such cases I just go with the flow and use whatever primer works best.
Modern primers are a marvel of ingenuity and production uniformity. The importance of these little cartridge "spark plugs" is often overlooked by recreational shooters--in itself a tribute to their reliability.
Copyright 2003, 2012 by Chuck Hawks. All rights reserved.