Primers

The handloader should understand that the primary function of a primer is to ignite the powder chargc prompdy, adequately and uniformly. What the primer may be made of, or any other spccial properties it may have in addition to its ability to ignite the charge, are incidental and of secondary importance. Emphasis may be placed upon ignition properties of a primer to the same degree that it is placed upon the function of the cartridge case as a gas seal. Both arc fundamental.

The type of primer that we arc most familiar with today and the one to which we will devote the most attention, is composed of three principal parts; a metal cup, a pellet of explosive priming compound which is pressed into the cup, and a metal anvil against which the priming compound is driven by the firing pin to explode it. This type of primer is a product of evolution and to understand the reasons for this type of design, its virtues and its limitations, it is necessary to know something of the general types which preceded it.

Our Civil War was fought for the most part with muzzle loading arms which were fired with percussion caps. These caps were made in a number of forms, but the most common and the best took the form of a thin copper cup having the priming compound pressed into it and usually covered with a thin disc of tin foil. This fitted tightly over a steel nipple on the barrel, with the priming pellet in contact or close to the top of the nipple. The nipple was provided with ^ a hole leading to the powder chamber and its upper edge was flat- When the hollowed face of the hammer struck the cap, the pellet was pinched between the bottom of the hammer cup and the fiat surface of the nipple, causing it to explode. The flash produced passed on to the charge, igniting it. It will be seen that this system had all the ele* ments of our present day primers; a cup, a priming pellet and an anvil against which the pellet was exploded.

The demand for arms during the Civil War period and especially for arras that could be reloaded more rapidly than the muzzle loaders, led to the development of the breech loader, the metallic cartridge and the repeating rifle, many novel breech loading systems making their appcarance in rapid succcssion. The first practical repeating rifle was the Spencer, which used a rim fire cartridge of large caliber.

Rim fire cartridge cases are made from thin metal ar.d in folding or forming the rim, a space is left into which the priming mixture is "spun," forming a ring of priming around the rim of the case. The firing pin must strike the cartridge at the rim in order to pinch the priming and tire it. This type of priming is unsatisfactory in large caliber cases. The ring of priming is brittle and structurally weak and in the ordinary handling and loading of the cartridges, pieces of priming break away, leaving dead spaces which, if struck by the firing pin, will result in mis-fires.

A lot of muzzle loading arms were converted to take the then new metallic cartridges and the design of some arms made it easier to convcrt them to fire a center fire cartridge. One type of center fire cartridge that enjoyed a short period of popularity was made with an internal primer. The case itself looked like a rim fire ease and the primer was in the form of a pellet, crimped into the base of the case, on die inside. But this type of case was not reloadable. The reload-ability of ammunition and the people who have reloaded it have had a great influence upon the development of our ammunition, not only in the past but at the present time 47 as well. Many a rcloadcr with a litde time and money at his disposal, plus the ability to experiment inteiligendy, has contributed to the development of factory loaded ammuni-don. Cartridges were expensive in the early days of the ammunition industry and money was scarcer than it is today, consequendy the reloadability of ammunition was important to the owner of any firearm. Even today there arc

Am early center fix© cartridge—made wrltb an internal prtraer.

thousands of shooters who, because of the expense or factory ammunition, would never purchase firearms were it not that they can easily reload their fired cartridge cases with a few simple tools and thus provide themselves with an abundance of ammunition at small expense.

The immediate forerunner of our present primers was what is commonly termed the "Berdan" primer, named after its inventor, a Colonel Berdan of the Union Army. This primer takes the form of a cup similar to that used in our present primers. This cup contained the primer pellet but had no anvil. The anvil was formed in the bottom of the primer pocket and was part of the cartridge case. Flash holes or vents were drilled at the base of the anvil and were usually two or three in number. The Berdan primer has certain points in its favor, perhaps the principal of which is that the anvil in the primer pocket, being of solid brass, is more rigid and offers greater resistance to the blow of the firing pin than the separate bent metal anvil which we now 4g use. But from a reloading standpoint the advantage is all the other way. Berdan primers are used almost exclusively in European ammunition, but it should be borne in mind that firearms were never used as extensively by the general population of European countries as here in the United States and consequently reloading has never attained the wide spread popularity that it has here. Europe was, as it is now, a collection of settled countries with fixed frontiers (as long as the politicians left them alone) while in the United Stales the condition was different.

At the time when firearms and ammunition were undergoing their most rapid development we were a new nation; one that had been hacked out of a wilderness and one in the development of which firearms had played a most important part. Furthermore, at that particular period, we had a rapidly expanding frontier towards the West, where firearms in the hands of the setders were indispensible tools. Our ammunition problem was different from that of Europe and the problem of reloading fired cartridge cases was an important part of it.

The Berdan primer did not meet the requirements of the rcloadcr satisfactorily. The anvil in the center of the primer pocket, with small vents around it, did not permit easy expulsion of the fired primers. They could not be forced out from ihc inside but had to be dug or pried out from the ouiside, which was inconvenient. The vents were small and were easily clogged by fouling or corrosion, the latter sometimes forming after the ammunition was reloaded. The early folded head cases had anvils that were merely pressed into shape, these were not of solid brass and a long firing pin would deform them and reduce their height. However, black powder is easily ignited and minor damage to Berdan anvils did not have any appreciable effect upon ignition. The objection to the Berdan primer from a reloading standpoint was chicfly a mechanical one, but with modern smokeless powders any damage to the anvils, whether from corrosion, erosion, or mechanical causes, will affect the order 49 of explosion of the primers. Any lack of uniformity of the anvils will result in variations in ignition and, consequently, in muzzle velocity. Early attempts were made to overcome the difficulty of dccapping cases by providing a central hole through the anvil, sometimes by itself and sometimes with vents at the base of the anvil as usual. The single flash hole through the anvil was unsatisfactory. In the first place, this design removes the support from the place it is needed most, that is, right under the point of the firing pin. In the second place, the flash produced by the primer was limited to that produced in the immediate vicinity of the flash hole, the indentation of the cup practically closing the vent. With

RIM FIRE. 5EP4RAIE AtfWlFRINE& uB£RDAN>RiMER

other vents at the base of the anvil the ignition was improved, but the central vent still failed to give sufficient support to the pellet and the anvils were subject to the same rigors of repeated firing and reloading. This idea of putting a central vent in a Berdan primer anvil has been "rediscovered" a number of times during the past sixty years, but it is fundamentally wrong and thus far has always ended up a failure. It does permit primers to be forced out from the inside of the case with the conventional decapper having a pin on the end for the purpose, but that is about the extent of its rather questionable advantage.

Now let's take a look at the American type of primer 5° in comparison, with its separate anvil assembled with the primer and one central flash hole in the primer pocket. Let us grant that this anvil is less firm and more likely to collapse under the blow of a firing pin than the solid Berdan type. The superb accuracy we obtain with our match ammunition would seem to indicate that there was nothing wrong with the ignition and that the objection referred to was purely theoretical but the answer is, that our anvils are too near the line of being unsatisfactory. They do collapse to a certain extent, cushioning the blow of the firing pin; also, unless they are properly made and hardened by cold work, they can cause ignition difficulties. Very well. We will give the Berdan anvil the edge in new ammunition but not in reloaded ammunition. Our primers are easily expelled; the primer pockets offer no irregularities but are easily cleaned of fouling to give new primers a firm seat on the bottoms of the primer pockets, and as each primer has a new anvil incorporated in it, it is possible to get uniform ignition regardless of the number of times that a case is reloaded. So much for general types of primers.

The reloader can do no more than purchase primers and use them. He can't make them and he can't change the ones he buys, so at first glance, it may seem useless to say much about the way they were made. Nevertheless, the primer is the very heart of a cartridge and the use of an improper primer or one that is improperly seated can defeat all the pains and care that you may take in reloading ammunition. And what is an improper primer? Simply one that does nor ignite powder charges uniformly and adequately. A primer that may be unsatisfactory with one load may be excellent with another charge of a finer or more easily ignited powder. Judging from an extensive correspondence with reloaders in this and other countries, the popular belief is that accurate ammunition depends upon extreme accuracy of powder charges and uniform bullet diameters and weights. Up to a certain point, yes, but primers can make a lot more difference in accuracy than any little differences in the weights of powder charges, and reloaded ammunition 51 that shoots fairly well can often be made to shoot better, simply by changing primers. It therefore seems permissible to look closely at the way primers arc made and why.

The Primer Cup. The function of the primer cup, in addition to holding the priming pellet, is to prevent gas from escaping to the rear. It functions in the primer pocket that same way that the case does in the chamber. Under pressure, the walls of the cup expand against the wall of its pockct, thus forming a gas seal. Primer pockets are not always perfectly round and even though primers seem to fit them tighdy there is usually enough space somewhere around them to permit air or water to enter, therefore commercial and military primers are waterproofed after loading, by allowing a little varnish or lacquer to flow around the edges of the primers to fill these minute crevices.

The cups must be soft and thin enough to be properly indented by the firing pins of the arms they are to be used in, at the same time they must be strong enough to hold in the pressures developed within them. The sensitivity of the priming mixture influences the design of the primer cup also. Some mixtures require a harder blow to explode them than others, with such, a thick or stiff primer cup might absorb too much of the blow of the striker to cause a proper and uniform explosion. If a mixture could not be fired with a cup strong enough to support the pressure developed, that mixture would have to be discarded. Therefore, the differences in hardness that is found between primers of different makes is not a matter of chance but is the result of careful study and experimentation on the part of the manufacturers. A primer having a stiff or thick cup is not necessarily better than one having a thinner and softer cup, except that the former can be seated with less liability of deforming it in the process.

Generally speaking, primers for rifle cartridges are made with thicker and stiffer cups and contain more or hotter mixtures than primers intended for use in pistol and revolver cartridges. The rifle primers are made suffer or thicker 52 bccause the firing pins of fifles usually strike harder blows than diose of pistols or revolvers. Furthermore, the pressures built up inside of rifle primers arc much higher than those developed in pistol primers so, if too thin or too soft metal is used in the cups, die primer will be pierced, permitting gas to escape through the action and possibly causing eye burns.

Pierced primers may be caused by too long or too sharp a firing pin, but the more common reason for them is failure of the primer cup at the point where it is struck. The cup is weakened where it is indented and if the pressure within the primer be too high, the weakened portion may blow back through the firing pin hole and permit gas to escape at the same time. When this happens, the striker or firing pin is blown back violently and may be damaged. Firing pin holes that have worn large or become eroded by escaping gns may not support the center of the primer sufficiendy and may permit a circular piece of the cup to blow out. This condition can often be detected by examining fired primers and observing the area of that part of the primer which has set back into the firing pin hole, in relation to the indentation of die firing pin. There must, of course, be a litde play around the firing pin in order to permit it to act freely and without sticking in its forward position, but the difference in the size of the hole and the firing pin should not be excessive. It is well also to examine the firing pin itself, as the trouble may be due to its wear rather than to the hole through which it passes.

The amount of pressure developed inside of the primer is influenced by the size of the vent. If the pressure within the case were maintained long enough, the primer pressure would be equal to the chamber pressure but the cycle of ignition and combustion is so short that there is not time for the pressure to equalize itself in these two cavities. In spite of this, the primer pressure will increase as the size of the vent increases.

Halved sections or a .30/40 case- which has been flred with a mercuric primer, then polished and etched. This case had spUt and stretched at the head» due to excess head space in the action.

Showing upsettage of bases of flat base bullets in comparison ™ * boat-tail bullet which does not upset when flred. Up-•ettage depends upon the structure of the bullet, its hardness, the force applied behind It and the suddenness with which the force is applied.

Was this article helpful?

0 0

Post a comment