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Primer seating primer.

* There's quite a bit more to the seemingly simple act of seating primers than meets the eye at first glance, and priming technique contributes more to the success of the handload than most folks think. Primer selection, of course, is the first step in the process, but let's assume that we already know the best brand and brisance of cap for the load in question. All that's left is poking one each primer into each pocket, ringt? Wrong.

Such random poking will, most of the time, produce a cartridge which goes bang when the trigger is pulled, but that isn't the end of the story. The primer is the initiator, the igniter, of the whole complex chain of events which occurs during the firing of a cartridge. If it fails, nothing happens. If it fires, but performs at substantial levels, something happens, but it's not good--from hangfires at best to a squib, at worst, which may even leave a bullet stuck in the barrel. The most common malfeasance-of-office of which the primer may be quilty, however, is undetectable by human sense, and is thus the most difficult to track down. The shooter may not even know he has an ignition problem, and blane bad results on the rifle, bullet, or powder, when, in fact, the trouble lies with his own priming tools and/or his use of them.

Most reloaders probably prime metallic cases with the equipment with which their presses came equipped, typically the swinging priming arm which works through a slot in the ram. This works, but it's a little like using a backhoe to get the crabgrass out of your lawn--too much machinery for the job. Most loading presses are simply too powerful and the linkages are designed for a different purpose.

Two exceptions are the Bonanza Co-Ax and the brand-new RCBS Big Max, both of which have special, overhead priming systems which allow the delicate primer-seating task to be accomplished with a bit more sensitivity.

There are all manner of special priming tools on the market from RCBS, Bonanza, Lee, and others which are designed especially for the task and which are worth the money. Some of these include a primer magazine tube which combines high-volume production with sensitive seating, but I must add that I personally prefer not to use any such device. The possibility of an explosion is extremely remote (especially with the Bonanza tube), but it does undeniably exist, and I have too much respect for the power of these tiny caps to run even a distant risk.

My choice is, in fact, the simplest and least expensive of all the primer-seating tools, the little thumb-powered Lee sans magazine. It's little slower than most, but provides excellent "feel." I keep several around the bench, set up with different shellholders.

To be entirely honest about it, I sometimes think a bit too much is made in the reloading press about this business of feeling a primer "bottom" in its pocket. More important to me is the ability to feel subtle difference in primer-pocket tightness in different cartridge cases as i seat primers. With the Lee tool, I can sense amazingly small differences, too small to reliably detect even with a good micrometer measuring head diameter, and this is useful information. It allows me to make judgements about the pressure levels of the loads last fired in the cases, and as to whether a case should be discarded rather than reloaded "just one more time." It is even possible to sort a batch of cases into different lots on the basis of primer-pocket tightness with such a low-mechanical-advantage tool.

Given pockets of proper dimensions, the important thing is that primers be seated neither too shallow nor too deep. If too shallow, part of the firing pin's energy must be used to push the cap deeper into its pocket, usually causing misfires. Such loads may fire on the second try, but ignition is sure to be erratic. Also, "high" primers can cause accidental "slam-fires," especially in semi-automatic arms, when the bolt goes home. It might even be possible for the gun to fire in this fashion before the breech is fully locked, which could be disastrous.

Primers seated too deeply result in the possible crushing or cracking of the pellet of priming compound, which also tends to give erratic ignition.

With tools on which the priming stroke ends against a positive stop, seating depth depends not only on the adjustment of the stop but also upon the combined dimensional tolerances of the shellholder and case rims. In other words, you need to remember that a readjustment may be required when changing calibers and/or lots of brass. The object is to get all primers seated uniformly, with the anvil "feet" pressed firmly against the bottom of each primer pocket. This should result in the primer cup's face lying a few thousands of an inch below flush with the case head.

At least one special micrometer gauge is made to determine that depth, but an experienced fingertip is more than sensitive enough to detect whether the primer face is above, flush with, or below the case-head surface, and roughly how much. Some variation in this dimension will result from a batch of cases in which primer-pocket depths vary somewhat, and some benchrest shooters use special tools to make pocket depths perfectly uniform. Their rifles may be accurate enough to reveal the benefits of such meticulous case preparation (although I doubt it, in most case), but yours and mine are probably not. Only a batch of cases with mixed headstamps would be likely to reveal enough variation to give problems . . . and anybody who mixes case brands and lots in the same batch of handloads is innocent enough (and little enough interested in real accuracy to begin with) not to notice.

With the exception of benchresting or, possibly, very specialized, long-range varminting, merely seating all primers to a uniform depth below flush will suffice, after having determined the correct depth for that particular lot of brass with the specific tooling available. In short, handloaded primers should look very much like those in unfired factory ammo. If they do, the final proof will be in the shooting. If they do not, chances are that sloppy or careless technique on the part of the reloader is at fault, rather than his tools, rifle, cases, or the primer manufacturer.
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Author:Wootters, John
Publication:Guns & Ammo
Article Type:column
Date:Aug 1, 1984
Words:1067
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