Wednesday, July 16, 2008

Priming the pump: Methods of case priming

In the previous three part ‘case prep’ articles we looked at preparing once fired rifle cases for hand loading.

Now, let’s look at the first step in the loading process; Priming the cases.

We’ll leave choosing the brand and type of primer for another time. In this piece we’ll concentrate on actually pressing the primers into the case.

There are many gidgets, gadgets, and required geegaws used in the priming process.

Simply making the initial decision of what tool to use can be exhausting
Here we’ll look at two basic types, each representative of a class.

Please note, this article deals only with single priming cases, not the whole process of progressive reloading and the complicated mechanisms used on those presses.


First up, and my personal favorite, is the LEE Auto Prime. Mine has been in constant use for many years, priming untold thousands of cases in that time. This type of tool is also made by RCBS and others, but the LEE is what’s on my reloading bench. Next week an RCBS version will probably join it, and my fickle heart will be lost once again.


The LEE Auto Prime requires the use of special shell holders, but the set is fairly comprehensive and not too expensive. Both the hand tool and the shell holder set can be bought new from Midway USA for under $25 together. The tool comes equipped with two interchangeable trays, one for large primers and one for small.

One of the useful features of this tool is the ability to prime cases without actually touching a primer. Primers can be easily contaminated, and skin oil is sufficient to damage the exposed priming solution. Primers are dumped straight from the box into the tipping/feed tray. (RCBS has the same feature on their tool)

Since the primers must be oriented correctly to be installed, the tray has concentric ridges molded into it. Gently rocking the tray back and forth will tip the primers over till they are all facing fire-side up.


From this position they will be fed directly to the primer installation ram press.


A cartridge case is slipped into the shell holder, which will place the primer hole directly over the ram. Light hand pressure is all that’s usually required to seat most any primer. Too little pressure and the pocket is oversized. If too much pressure is required then something is interfering with the seating process. Once the correct pressure is determined, every slightest change in seating quality becomes obvious to an experienced hand.

To me, this represents the largest benefit to this type of primer seating tool.
The ‘feel’ of seating the primer can make problem cases obvious. Primers seated short, or too deep, stand out like a sore thumb.

Cases that have had their primer pockets massaged as shown in the ‘case prep’ articles usually seat every primer exactly the same, nicely.

There is a shield that installs over the primer tray, and it should be left in place while in use.


While using the LEE Auto Prime, or during *any* priming operation for that matter, eye protection should be worn. Accidents can and will happen, and primers can be touchy things. While I have never had a primer fire during seating, there are reports of it happening. Better to be safe than sorry. In fact, I make a point of aiming the priming tool away from my face as I seat a primer.

It should be noted that LEE specifically states Federal primers are not to be used in this tool, and reduced quantities of other primers are to be loaded at one time.

The next genre of priming tool examined is what I call the ‘press ram priming tools’. These mount in a reloading press and use the ram stroke to seat the primer.

The only advantages to these tools I can think of is they always use standard shell holders, and usually the tool comes as part of every press kit.

The press ram-prime tools I own, an RCBS and a LEE, both came ‘free’ with new presses I’ve bought over the years. I’ve never used the LEE version, but the RCBS tool gets used often with my 7.62x54mm loading. Why that case? Because I don’t have an Auto Prime shell holder in that size, but do have a standard shell holder.


Both the RCBS and the LEE come with interchangeable tool heads for small and large primers, but the RCBS is clearly better built of finer materials.


In using the RCBS press priming tool, one piece of reloading equipment must be cleaned, as it will matter now. The shell holder is used as part of this tool and the primer is fed through the center of it. It must be cleaned or the dirt accumulated over years of reloading will migrate to the primer pocket.


Following directions, the tool is set up so the primer ram just comes through the base and seats the primer. I recommend seating the first one very carefully till it’s just right, then dial the shell holder and base down on the ram (with the properly primed case installed) so every succeeding case is primed the same way.



It should be noted the average press has *massive* power compared to what’s needed to seat a primer. My own RCBS Ammomaster loses all feel as to how the primer is entering or seating in the pocket. In fact, just dropping my press handle the last six inches of the stroke usually seats the primer just fine. The handle alone is heavy enough to do the job.

In using a single feed priming tool like this RCBS, the primers must first be dumped into a flip tray and aligned properly. Then each primer is picked up and set into the ram prime. I prefer to have the ram raised all the way when I charge it, sticking up through the shell holder. Then I lower the ram just enough to slide in a case, and seat the primer with a finger or two’s worth of pressure.

An important note: Wash your hands before handling any primers!!


Great care must be taken, no matter what kind of tool is being used, to get primers properly seated. Never leave a primer seated above the surface of the case, and usually seated a bit below the surface is better.

Primers seated high are a common cause of slam fires and firing out of battery.

This mean gun go BOOM when you don’t intend it to. That’s bad; real bad.

If a primer is found to be too high, it can usually be put back into the tool and carefully adjusted. This problem is not often encountered when primers are seated by hand, but progressive presses have a bad habit of giving us high primers some times.


The one on the left is obviously too high, and must be corrected.

As each case is primed, I like to set the case mouth down in a loading tray.

Why? Just to be sure nothing falls in the case, and to discourage any moisture from finding it’s way to the exposed primer. While unlikely to be an issue on most loading benches, why take the chance?

Our next step will be charging the case with powder, followed by seating a bullet. Each step is worthy of it’s own article and will be covered in the future as we load these 8x57mm cases together.

Cheers friends, and keep your primers dry!



pdb said...

Thank you for doing this series!

I'm gearing up to make match quality 7.62x51 for my M14, and these posts have been awesomely informative.

Weetabix said...

Ditto the thanks!

Do you contemplate, as a part of the series, an article on the minimum set of tools necessary to start reloading?

Carteach0 said...


As it happens, I am considering putting together a traveling reloading setup. One which would fit inside a medium size tote. If I do so, it actually be a simple but decent quality beginners setup.
If I do so, I will write it up and post here.....

Weetabix said...