This pierced primer in a .38 Super round (right) has a hole in it the size of the tip of the firing pin. Other pierced primers might have just a small cut in the firing pin indent, but they can be identified by black carbon fouling on the primer where gases have escaped.
October 09, 2024
By Brad Miller, PHD
Pierced primers are bad. You already know this if you’ve experienced one. A blast of hot gas to the face is a good reminder of why we wear eye protection when shooting. A pierced primer is often associated with being a sign that pressure is too high. Pierced primers also can be caused by excessive headspace. And another cause of pierced primers is a rough or damaged firing pin. The ideal firing pin surface is smooth and rounded. Rough surfaces can score the primer and weaken the metal, and that’s where it will fail.
The firing pin shown here is heavily eroded by hot gases, and the firing pin hole in the frame appears to be etched as well. A firing pin in this condition will only increase the number of pierced primers and pro- duce more damage. It must be replaced. What some people are not aware of is the damage a pierced primer can do to their gun. Cartridges operate at extremely high pressures. Peak operating pressures range from 14,000 to 65,000 psi, depending on the cartridge. Leaking even a fraction of that super-hot gas pressure somewhere it shouldn’t be can erode metal.
This comparison photo shows a damaged firing pin (left) compared to a new one. The eroded firing pin is shorter because metal has been jet- blasted away. Note the smooth, rounded nose of the new firing pin. The usual victim of a pierced primer is the firing pin because the gas escapes right at the point of damage. The introductory photo shows an example of an eroded firing pin in a revolver that resulted from pierced primers. It is from a .357 Magnum S&W revolver, and as most readers know the .357 Magnum is a high-pressure cartridge. (The maximum pressure limit is 35,000 psi.) As the photo shows, the firing pin is damaged. The revolver’s frame also shows erosion damage to the sides of the firing pin hole.
The eroded firing pin made an ugly-looking strike on the primer (right). The primer shows evidence of flow back into the eroded area around the firing pin hole in the frame. A normal-looking firing pin strike is shown to the left. Firing pins on some guns can be replaced easily, like this S&W revolver with a frame-mounted firing pin. It’s not so easy for other guns and might require a gunsmith. Some damaged firing pins can be fixed, depending on the extent of damage. They can be sanded down with fine sandpaper to return them to a proper smooth, round profile, but that only works if the firing pin is still long enough to fire the round. If you have experienced pierced primers, check out your firing pin and breechface for damage. The firing pin might need replacement or repair.
Advertisement