Reloading Basics Part 3: Primers
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- Last updated: 29/06/2018
Primers are by far the most dangerous of the components used in the reloading process, due to the fact that they are required to be impact sensitive. They should therefore be handled with care and treated with respect. Always wear eye protection when you are working with primers.
The modern primer consists of a metal cup containing the priming compound, which is held in place with a paper seal to protect it from moisture. The paper is in turn held in place by a tiny, three-legged, metal anvil, usually made of brass. Before a primer is seated into a case, the feet of the anvil can be seen to project very slightly from the edge of the cup. When the primer is inserted into the primer pocket of a case, these feet come into contact with the bottom of the pocket and are forced further into the primer cup as the primer is seated fully. This acts to compress the priming compound and so prepare it for ignition. When the firing pin strikes the primer, it ignites the tiny charge of a highly explosive compound, which in turn ignites the much larger powder charge inside the cartridge case.
Different primers are available for pistols and for rifles and both types come in two basic sizes; small, at 0.175-inch diameter, and large, at 0.210-inch diameter. The rifle primers are slightly deeper, to fit the deeper pocket in the rifle cartridge. Rifle and pistol primers are not interchangeable. As well as being deeper, rifle primers carry a much larger charge of priming compound and could cause dangerous pressures if used in pistol cases. Pistol primers would seat too deeply in rifle cases and would cause poor, uneven ignition. Other types of primers include magnum primers, which contain increased amounts of priming compound and should only be used where reloading data specifically requires them, and Benchrest primers, which are manufactured under tighter tolerances to give increased consistency.
Despite their size, primers can be extremely dangerous and should be handled and stored with care. They will explode with unbelievable violence if subject to a sharp impact or shock. Priming compound is manufactured in very small batches, even in the largest manufacturing plants, because it is so volatile. The manufacturers then go to great lengths to pack them into protective cartons, intended to keep the primers from coming into contact with each other, to prevent a sympathetic detonation of a whole carton or box. Do not be tempted to take them out of their cartons and store them loose in a box or tin. Take a look at the packaging on Federal primers and you will see it is substantial to say the least; they would not go to that trouble and expense if it wasn’t absolutely necessary. Keep them in their original packaging and only take out as many as you need for your immediate needs. Primers can be stored for a considerable time without any deterioration, so long as they are kept away from damp conditions or extremes of temperature. I recently started using some Remington primers that I have had for more years than I can remember (the prices on the pack is £16/1000 and they are now over £50) and they work just fine.
There are a number of different brands of primers, and although they all perform the same function, each will ignite the powder charge slightly differently and so affect the performance of the completed rounds. In my experience, I have found the difference to be barely noticeable in most applications and the choice of brand is more often down to price and availability than performance.
Most reloaders seem to just stick with the brand of primers they first start reloading with, and this is a good practice to adopt. In the good old days of competitive pistol shooting, most shooters favoured Federal primers, simply because the softer cups were more easily ignited by the highly tuned and light hammer blow of their pistols. For the foregoing reason, Federal primers were usually far more expensive than other makes but that price gap has now pretty much disappeared and all makes are very similar in price. For use in the types of rifles and carbines we use today, all of the brands usually work absolutely fine.
There are many different primer seating tools available to the reloader, some press mounted and some hand-held, and I will look at them in more detail in later. The principal of primer seating is however, the same whatever the tool you use. Primers are either placed into the tool individually, by hand, or fed into it via a tray or tube. Once the primer is in position under the case, a ram will lift it into the primer pocket and seat it. The most important factor in this operation is the use of the correct amount of pressure to seat the primer. Too much force will squash the primer, crushing the priming compound and often resulting in a misfire. When too much force has been used to seat a primer, you can see that it has been flattened and the edges have lost some of their radii. Too little force may leave the primer sitting proud of the case head, where it could be accidentally ignited when the action of the gun is closed, an occurrence known as a slam fire. With practice, you will develop a ‘feel’ for seating primers correctly. There is a very detectable, firm and solid stop when the primer has fully travelled into the primer pocket, and further force will only serve to flatten it.
Like so many aspects of reloading, it is simply a case of practicing and watching for signs of problems. With tube fed priming tools, and to a lesser extent with tray fed tools, great care is needed to avoid one primer detonating and triggering a sympathetic detonation of all the other primers in the feed system. For this reason, the user instructions should be read carefully and, in my opinion, tube fed tools should be avoided at all costs. More on this in future articles.
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