When a gun misfires, in other words we pull the trigger and get a click instead of a bang, the cause is typically one of a short list of things: (1) we’ve lightened springs, in pursuit of lighter trigger pulls, to the point the firing pin has insufficient impact energy to pop the primer, (2) we’re using ammunition with really hard primers; some foreign ammo has primers so hard I’ve seen misfires in Glocks even with factory firing pin springs, (3) probably most common, with handloads, we have not fully seated the primer.
A primer consists of a little metal cup containing a piece of metal called an anvil. The anvil has a flat part that, when it’s inside the cup, is parallel with the flat portion of the cup, then the top of the anvil has three outward-radiating holes in it. Look down inside a primer, the top of the anvil kind of looks like a radiation symbol. Inside the primer, between the cup and the anvil, we have priming compound. This is a pressure-sensitive, explosive material – in other words, you hit it and it explodes, generating fire in the process.
When the firing pin hits the primer, it mashes the priming compound between the cup and the anvil; the priming compound ignites, the flame pours out through the holes in the anvil, through the flash hole (a circular hole at the bottom of the primer pocket) into the interior of the case, which ignites the gunpowder. As the gunpowder burns, it gives us a large quantity of expanding gas which, when it’s contained inside the cartridge case, which is surrounded and reinforced by the steel chamber, generates thousands of pounds per square inch of pressure, which serves to propel the bullet down the barrel and out of the gun at hundreds or even thousands of feet per second.
As the primer sits there in the primer pocket, it needs to be fully seated. That means the top of the primer is not just even with the base of the case, it’s actually slightly below the base. We call this “seating below flush.” If the primer is not fully seated, if there is a gap between the primer and the bottom of the primer pocket, when the firing pin hits the primer it will drive the primer forward into the primer pocket. This absorbs enough impact energy we get a misfire.
When the primer is not fully seated, instead the top of the primer is sticking up above the cartridge case’s base, we call that having a “high primer.” In addition to making the ammo prone to misfires, it has not been unknown for the breech face, as the gun is cycling, to smack a high primer hard enough the round fires as the gun goes into battery, i.e. as the action closes. This is bad.
SAAMI calls for primers to be seated flush with the case head to .008” below the face of the case head.
As you’re case gaging your ammo after loading it, take a moment to visually inspect the primer, you should see it’s actually seated below flush. Run a finger over the base of the case; can you feel a “lip” where the edges of the primer pocket, surrounding the primer, are significantly above the top of the primer? Do this for every round you handload, and you can avoid that frustrating experience where you gun goes click instead of bang, or goes bang when you didn’t expect it. At least when that’s caused by high primers.
