Primer Myths

Primer Myths

Charles E. Petty

One of the most persistent myths in shooting is that there are hard primers and soft primers. That isn't true. The real issue is primer sensitivity or - more frequently - something within the gun or loading process that causes the gun to go click when it shoulda' gone bang.

All four of the major ammunition companies make primers and they all do it pretty much the same way. Thin brass and steel in huge rolls is bought from a mill. From it, primer cups and anvils, respectively, are stamped by simple presses. Everybody does it this way. A soapy lubricant is used in the stamping operations, both cup and anvil are then washed, dried and sent off to become primers. Some primer cups receive a thin nickel plating.

While there may be some small differences in specifications for the raw brass from one maker to the other, none of it is hardened - it couldn't be stamped right if it was. It is common knowledge that brass work-hardens with bending, but the only place that could happen to a significant degree would be along the radius where it rounds out from bottom to sides.

There is no need to worry much about hardness in that area since it isn't where the firing pin strikes. There have been instances where that area became so hard as to be brittle, and there could be a tiny perforation when the primer was fired. Some manufacturers include an annealing step to prevent that possibility.

But since there is no "work" done to the bottom of the cup, it is much less affected and remains essentially as it came from the mill. Still, everyone who reloads has probably experienced a misfire, and found that the firing pin impression on the primer was much smaller than normal. It is perfectly reasonable to think that individual primer was hard, but the trouble can almost always be traced to other causes. Very often, that primer will fire if it is hit again.
A common reason for that type of misfire in semi-automatic firearms is that the gun was not fully into the battery position. Semiautomatics, regardless of the type, must have a part called the disconnector that prevents the gun from firing out of battery. But if the slide closes almost all the way, the disconnector may allow the hammer to fall. Then a substantial portion of the firing pin's energy will be absorbed simply in pushing the slide into battery. That can almost always be traced to a dirty gun, but sometimes a weak recoil spring is the culprit. It can also be a shooter-induced malfunction by either "limp wristing" the pistol or by restricting slide movement with a faulty grip. The most common cause of misfires in revolvers is a weakened mainspring - often as a result of an effort to reduce the trigger pull. Those misfires are characterized by a light hit on the primer.

Stories of hard primers are much more commonly told by handloaders than shooters of factory ammunition. . The major cause of misfires in handloaded ammunition is a fault in the primer seating operation. What's ideal is for the primer to be seated so the anvil is just touching the bottom of the primer pocket. In practical terms, that means the primer should be 0.003" - 0.005" below flush with the head of the cartridge. If it isn't, the resulting "high primer" may misfire since the firing pin's energy is absorbed seating the primer the rest of the way.

It is also possible to induce a misfire by seating the primer too deeply. Many priming tools are capable of actually crushing the primer. If that happens, it is possible the primer mix inside the cup fractures or pulverizes, and if the primer mix cannot be compressed by the firing pin strike, a misfire is the result.

While the primer is the spark plug that gets things going, it is also the stopper that keeps the genie in the bottle. Its equally important other job is to seal the primer pocket so the pressure has to push the bullet down the bore. This obturation function is just another reason why primers can't be too hard. Since hardened brass becomes brittle - which would be a bad thing - it is in the interest of the manufacturers to prevent primer cups from becoming too hard.

The primer's malleability is the property that often leads reloaders astray. We are always told to watch for signs of high pressure by observing the fired primer. All primers have a radius between the flat bottom and side wall. A change there is taken to be a pressure indicator. And so it is, but there is substantial evidence to show that by the time the primer is noticeably flattened, pressures already are well above maximum. Other things reloaders look for are a diminished firing pin imprint, cratering around the firing pin impression or the smearing of primer metal outside the primer pocket. In more egregious cases, there will be enlargement of the primer pocket and possibly leakage around the primer. Those are signs that are far more serious and proof positive that the load is over maximum pressure. In the very worst case, the spent primer simply falls out.

In locked-breech semi-automatic pistols, there is a sign that can be misunderstood, but is indirect evidence that a load is too hot. The short recoil design common today allows the slide and barrel to recoil as a unit for a short distance before the barrel unlocks and drops down to let the slide continue in recoil. It is something that happens very quickly, and sometimes it is so fast that the firing pin does not have time to retract back into the slide before the barrel begins to drop down. The result is a primer with an elongated firing pin impression and, in a worst case, primer metal can actually be sheared off. While there are other causes, firing pin drag along the primer is often an indication of an excessive load.

As with all other things in shooting, the equipment we have today has evolved sequentially as one advance opened the door for the next one. As an example, in the early 1800s the Rev. Alexander John Forsyth - a Scottish minister - found that certain chemical compounds, among them fulminate of mercury, could be made to detonate with a blow. Within just a few years, the flintlock rifle was made obsolete by the percussion cap. One of the drawbacks of any muzzleloading firearm is that there has to be a hole somewhere to permit ignition. It must have been one of those "eureka" moments when someone figured out that a primer could also seal the breech end of a cartridge case. It was immediately more efficient. In his Complete Guide to Handloading, The American Rifleman's Phil Sharpe wrote, "There is more real romance wrapped up in the little primer of your cartridge than in any other single development of firearms science." Primer development knew no national boundaries, but American and British efforts were quickly accepted as standard. Interestingly, the Berdan primer, which is used everywhere but the U.S., was an American invention, and the Boxer primer we use came from Great Britain.

Very early in the history of cartridge cases, standardization came about in the form of large primers with a diameter of 0.210" and small ones at 0.175". In addition, there was distinction between rifle and pistol primers since the powders used in handgun cartridges rarely needed as energetic a mix to get them going compared with rifle loads. That picture becomes even muddier when we add magnum primers to the equation. Both the quantity of primer mix and its chemistry are the controlled variables that make this work.

While the diameters of both rifle and pistol primers are the same, the height is not. It is not unusual to see small rifle primers loaded in handgun cases for exceptionally high pressure loads. Examples would be the super magnum handgun rounds, such as the .454 Casull, which typically uses a small rifle primer. Another would be their use in cartridges such as handloads for the .38 Super when pumped up to make major velocities in practical shooting. But that doesn't work with large primers. The large rifle primer is too high to seat in a pistol case.

The primer mix is made on site and usually has a greenish color. The consistency when wet is similar to modeling clay and as long as it remains wet, the mix is relatively stable.

Primer manufacture is done with a series of plates that typically have 500 holes of the proper size. One is filled with cups and another with primer mix. That part of the process is done in a separate cell. The operator puts a ball of wet mix on the charge plate and then spreads it evenly with a rubber squeegee to fill all the holes. Actually, this is a very skilled position because the operator must be very consistent. The amount of mix is a variable but runs around 20 to 40 milligrams per primer. The charge plate is then mated with a plate full of cups and the wet mix pushed down into the cup. Commonly, a foil sealer is put on top of the mix and then the anvil is inserted. This operation is called "booking" and in some plants is done by very gifted folks who hold a plate full of charged cups in one hand and a plate full of anvils in the other. Like closing the pages of a book the two are deftly brought together. Other plants use a different style plate and simply sit it atop the cups and then pull out a spacer to drop the anvils in place. The assembled pieces go into a press where the anvils are seated to the proper depth.

There really are two different issues for the manufacturers. Primers can be too sensitive, which could pose shipping problems, so there is an industry standard test for primer sensitivity. It's call a drop test. A primed case is placed in a fixture with the appropriate chamber that has a movable firing pin also of standard dimensions. A steel ball that weighs either two or four ounces, depending on the type of ammunition being tested, is suspended above the firing pin and held in place by an electromagnet. The height of the ball is variable. Depending upon the cartridge, there are three positions with different heights: no-fire, all-fire and half-fire. Typical no-fire heights are usually around 2" to 3". All-fire heights are more variable and range from a low of 15" to as much as 25". The half-fire height is determined by statistical analysis with a typical value being 5" or 6". Each manufacturer has its own parameters to judge the acceptability of a primer lot, but the test might use 25 primers at 1" intervals from the no-fire height until reaching a point where all of them pop. If that sounds complicated, that's because it is.

Where it gets interesting is when you try to find comparative test data for the different brands. Nobody in the industry is talking. Obviously, the makers test competitor's products, but the only on-the-record response I could get was from a Remington executive who said, "there isn't much difference" in primers.

Hard primers are the stuff of mythology. It's kinda' like the wonderful Pogo comic strip of years ago, "we have met the enemy and it is us," said Pogo. It is easy to place the blame on a hard primer when doing so saves us from admitting that there might be something wrong with our reloads.

Copyright 1998-2014 Stephen Ricciardelli