It may be the single-most influential reloading component, so learn all about it: the primer! READ MORE

rifle primer

Glen Zediker

This is one component in the collection that might not get all the attention it warrants. That’s because it is the one thing, above all other components, that you don’t want to just swap and switch around.

We’ve all heard cautions about testing new lots of every component, especially propellant, but primers not only change lot to lot, they vary greatly in their influence on any one load, brand to brand. The difference in one brand to the next can equal a good deal more or less pressure, for instance. While there are “general” tendencies respecting the “power” of various-brand primers, always (always) reduce the load (propellant quantity) when switching primers.

This has become more of an issue over the past few years as we’ve faced component shortages. I can tell you without a doubt that going from a WW to a CCI, or from a Remington to a Federal, can have a major influence on a load. I establish that from chronograph readings. No doubt, it’s best to have a good supply of one primer brand and lot that produces good results, and when that’s not possible, it’s a hard sell to convince someone to stop loading ammo and get back to testing. But. It is important. I can tell you that from (bad) experience. How I, and we all, learn most things…

When I switch primers, whether as a test or a necessity, I reduce my load ONE FULL GRAIN. There can be that much effect.

The Thing Itself
A primer is made up of a brass cup filled with explosive compound (lead styphate). Lead styphate detonates on impact. Primers don’t burn – they explode! In the manufacturing process, this compound starts as a liquid. After it’s laid into the cup, and while it’s still wet, a triangular piece or metal (the “anvil”) is set in. When the cup surface is struck by the firing pin, the center collapses, squeezing the explosive compound between the interior of the cup and the anvil. That ignites the compound and sends a flame through the case flash hole, which in turn lights up the propellant.

Primers are dangerous!

Don’t underestimate that. I’ve had one experience that fortunately only created a huge start, but I know others who have had bigger more startling mishaps. These (almost always) come from primer reservoirs, like fill-tubes. Pay close attention when charging up a tube and make sure all the primers are facing the right way, and that you’re not trying to put in “one more” when it’s full! That’s when “it” usually happens. What will happen, by the way, is akin to a small grenade. Static electricity has also been blamed, so keep that in mind.

primer tray
Take care in filling primer tubes! Make double-sure all are facing correctly, and a good primer tray helps. This photo shows the correct orientation for using primers one at a time. To fill a primer tube, make sure the “shiny side” is facing up! Flip the tray over.

Sizes and Types
Primers come in two sizes and four types. “Large” and “small”: for example, .223 Rem. takes small, .308 Win. takes large. Then there are pistol and rifle in each size.

Rifle primers and pistol primers are not the same, even though they share common diameters! Rifle primers should have a tougher cup, and, usually, a hotter flash. Never swap rifle for pistol. Now, some practical-style competitive pistol shooters using their very high-pressure loads (like .38 Super Comp) sometimes substitute rifle primers because they’ll “handle” more pressure, but they’ve also tricked up striker power. That’s a specialized need.

Further, some primer brands are available with a “magnum” option. Some aren’t. My experience has been that depends on the “level” of their standard primer. A magnum primer, as you might guess, has a more intense, stouter flash that travels more “deeply” to ignite the larger and more dense powder column. It reaches further, faster.

large rifle primers

large rifle magnum primers

There’s no real reason not to experiment with “hotter” and “colder” primers, whether the case is stamped “mag” or not. Keep in mind that the experiment is all about the initial flash effect. And keep in mind that this (without a doubt) demands a reduction in the propellant charge at the start.

Over a many years I’ve seen some tendencies respecting flash effect. Using routine cartridges, like .308 Win., single-base extruded propellants tend to shoot well with a cooler spark to start, and the double-base, especially spherical-types, seem to respond best to a hotter flash. Many seem to think that the coating (necessary to form the spherical) and the inherent greater density (less air space between granules) in a spherical demands a little faster start.

Flash consistency is very important, shot to shot. The consistency of every component is important: bullet weights, diameters, case wall thicknesses, and all the way down the list. We’re hoping to get more consistent behavior from a “match” or “benchrest” primer, and we’re paying more for it. I can tell you that some brands that aren’t touted as “match” are already consistent. That all comes from experience: try different primers, just respect the need to initially reduce the load each test. I can also tell you that my notes tell me that the primer has a whopping lot to do with how high or low my velocity deviations plot out.

One last: there are small variations in primer dimensions (heights, diameters) among various brands. These variations are not influential to performance. But! Small diameter variations can influence feeding through priming tools. This can be a hitch especially in some progressive loading machines. Manufacturers usually offer insight (aka: “warnings”) as to which are or aren’t compatible, so find out.

Check out Midsouth products HERE
Primer trays HERE

This article is adapted from Glen’s books, Handloading For Competition and Top-Grade Ammo, available at Midsouth HERE. For more information about other books by Glen, visit

11 thoughts on “RELOADERS CORNER: Primer Tech”

  1. Razer good article about primers. Yes, there are a very important component and consistency is important especially in long range shooting.
    One area that was not mentioned was the hardness of the primer. Some of my revolvers have lightened springs to reduce trigger pull and will only function well with federal. Try CCI primers and one out of six will not ignite.

  2. I never understood why some primers come packaged laying on their side. This makes loading the primers into flip trays aggravating to the max. CCI packaging is the best I’ve found. I like gently laying the primer container open side up and gently turning the container onto the smooth side of the flip tray to see 100 primers lined in 10 neat rows of 10 each. Can’t do that when the primers are packaged laying on their side.

    1. Lee primer trays took care of this problem, their trays are ribbed and a lite shake and all are correctly oriented.

      1. Lee’s primer trays do not solve the problem. I challenge you to flip the primers from packages that have primers laying on their side into ANY primer tray and have them land in 10 rows of 10 primers each. When you solve the problem of defying gravity, let me know.

  3. Hey! How about showing us some actual data on pressures or velocity that reinforces the notion that primers aren’t as consistent as we’d like them to be, as the article insinuated?

  4. Thank you for this great article on primers. You have raised more questions for me. Why is there not a source to tell us all the specs on all the primers like there is with powders? Such as heat of explosion, hardness of cup and harmful ingredients such as lead and mercury so we can make informed decisions based on real facts not just the best looking packaging or price. I like making educated decisions based on as much fact as possible for my purpose then the price becomes irrelevant.

    1. I agree. We know a lot more about propellants from manufacturer data but not primers. Only primer data I’ve seen has been independent.

  5. I buy primers on a regular basis so as prevent using ‘old’ primers. Is my concern about using ‘old’ primers unjustified. I recently tested Winchester primers manufactured around 1980 (from a friend) which seemed to function perfectly.

    1. I’ve had some for years that, by my chronograph at least, haven’t changed. Storage is the big key, just like with propellants. Air tight, no extremes.

  6. Primers DO NOT ‘explode’. They create a flame which is totally different that an explosion. If they did in fact explode, there would be nothing left of the primer after it was struck by the firing pin.

    1. They are explosive when they’re in a primer tube. I know technically you are right but they detonate with an explosive impact.

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